Case 1 - The Haunted Island
Spooky ghosts have infested poor Martin's island and he needs your help, as the ghost scientists he hired haven't been able to crack the case in the two weeks they've been there!
Start by going towards the phone directly in front of you and interact with it when it starts ringing. This will initiate a conversation between Frog Detective and the Supervisor, who will tell you all about the case.
Once the call has ended, turn around and go to the table next to the door and interact with the magnifying glass to pick it up, you'll earn:
One achievement down, now it's time to head to the island. Interact with the door handle, and you'll be met with a title sequence introducing you to the characters you'll meet on the island.
Once you regain control, ignoring the monkey waving in front of you, turn around and interact with your boat to earn:
Now you can go to the left and speak with Larry, who will tell you that he knows the ghostly noises are coming from the cave in the forest. To be able to investigate this cave, you'll need an explosive device to clear the cave-in. For Larry to make the explosives, he'll need: toothpaste, some wool, a chunk of pure gold, and some pasta (very normal materials for a very standard explosive recipe).
First, we'll get the toothpaste. After speaking with Larry, make your way through the trees in the middle of the island and speak with Mo on the left. Select the You're nervous... option, and Mo will inform you that they want to impress MysteryMonkey at the dance competition. He'll want to know what type of dance will impress them the most.
We can now stop rudely ignoring the waving monkey on the beach and after some introductions, you can select the Dance styles... option to get the information Mo wants.
Go back and speak to Mo, selecting the Dance styles... option. When you are done speaking, you'll get Mousewash mouthwash.
Now go back around to the left and past Larry, you'll find Fresh X laying on a sun lounger. Speak to them and select the Your smile... option and he'll ask for something to keep his teeth clean, in exchange for the toothpaste. Now select the Mouthwash... option and he will give you the toothpaste.
Next up, we will get the wool. Grab the broom from the back of the centre area to the right of Mo, then turn around and to the left you'll find Noodle. Go speak to them and select the Your wool... option, they will ask you for a broom, which we have already acquired like the good investigator we are. So next select the Broom... option and you'll receive the wool.
Now we will get the gold. For this, we just need to speak to Martin, the sloth king of the island back in the centre area. Speak to him and select the Your nerves... option. After a nice calming visualisation exercise, he'll give you the gold.
Finally, we can get the pasta. Go to the table by Noodle and pick up the magnet. Now go see the Koala swimming in the sea and they'll ask for a magnet, which we have once again proved our detective prowess to acquire, before even knowing why we needed it. Select The magnet... and in exchange for the magnet, you'll get a shell. Now speak with Orbit back in the centre area. Select the Tiny Shells... option, followed by the Big Shell... option, and you'll get a magnifying glass. Finally, go back to where Larry is and speak with Bernie next to him. Select the Secret agent... option, then the Magnifying glass... option, to get the pasta.
Now that we have all the ingredients for explosives, we can go speak to Larry. Select Explosion..., then Yes! and you'll earn:
You'll now be in the cave, make your way forward and speak with Finley to earn:
After speaking with Finley, you'll emerge from the cave together and speak with Martin about the cause of the spooky noises. After some credits, you'll be asked to judge the dance competition. Once everyone is finished, you'll be presented with a menu asking you to pick the winner. Regardless of who you pick, you'll earn:
Lastly, you'll be back at the office and the phone will ring, answer it to unlock:
And that ends the first case!
Case 2 - The Case of the Invisible Wizard
An invisible wizard has moved into the town of Warlock Woods and someone has destroyed the welcoming parade made for them!
Start by answering the phone when it rings and the supervisor will give you the rundown of the case. Once the conversation is done, pick up your magnifying glass and go to leave as you did in the first case and you'll get to meet Lobster Cop, who will give you a notebook. When the conversation ends, go into Lobster Cop's office and interact with the notebook, put some stickers on it and when you are happy, select I'm done and Yep. You'll earn:
Now leave Lobster Cop's office and go through the door at the end of the hallway, you'll go through a title sequence similar to the first case.
One of the achievements for this case requires you speak with everyone and exhaust their dialogue so you can complete the notebook. I will be assuming from here that you will be doing just that.
Before we attempt to solve anything, we'll get a missable achievement out of the way. Go to the right and pick up the pie between the two houses (Pie 1/5), then speak with Victor in the hot tub behind the house on the right. After speaking with him about the wizard, you'll be given one money (Money 1/5). You should now have the option: Give item (lost pie) - he will refuse as you found it on the floor. You'll earn:
GROSSWhat were you thinking?!
To help everyone, there will be a chain of items from one character to another, so I suggest speaking with everyone in the town to get their notebook entries and what they all want. Starting from the entrance, in clockwise order, you'll speak to: Susan, Noddy, Mary, Carlos, Mandy, and Ralph.
Now that you've spoken with everyone and found out what they all need, we can start collecting the items. First, we'll collect up the pies for Mandy. The next pie is on one of the lanterns behind where you started from (Pie 2/5), while the third pie is on the left side of the stage in the middle of the area (Pie 3/5). You'll find another pie in a flower pot in front of Mary's house (Pie 4/5). The last pie will be under one of the tables at Carlos' shop (Pie 5/5). Now you can go and return these pies to Mandy, you'll receive one money (Money 2/5) and a fresh pie.
Now go give the fresh pie to Victor and you'll get a party hat. Give the hat to Carlos and in return you'll get one money (Money 3/5) and a rug. Before moving on, now that we have three money we can buy something from Carlos' shop to earn:
You'll be interrupted by the developer, who will refund the money you so recklessly spent. You'll get a picture of her in your notebook, which is required for a complete notebook.
You can now go and give the rug to Noddy, who in return will give you building supplies and one money (Money 4/5). Go and give the building supplies to Ralph and he'll give you the last money (Money 5/5) and a hook which you can give to Susan. She will give you access to her phone, but first go and see Mary so she can successfully extort you, then you'll get a phone number. Go back to Susan's house and use the phone to call the Mysterious Number. You'll speak with Barney, who'll tell you to check the entrance to the woods. There you'll find a pair of glasses on the floor belonging to the Invisible Wizard.
Before moving on, make sure to check your notebook, the only entry missing should be the Invisible Wizard. Once you've made sure you have all the entries, go to the house to the right of Carlos' shop and enter. You'll find the wizard behind some boxes in front of you, they'll then disappear and you'll find them again by the right wall behind more boxes. The wizard will disappear yet again, this time behind the boxes on the left side of the room. They'll disappear one final time through the door that was closed on the left wall, go down the stairs and speak with them. Once you've finished, you'll get the final entry and unlock:
Now you'll have to decide to either tell the truth, or lie about what happened.
Selecting Evil Guy did it will unlock:
While selecting Lola did it will unlock:
SNITCHFaced a big moral dilemma.
Once you've made your choice, you can either play it out until the end and speak with the Supervisor (who will commend you for solving the case, or scold you for lying if you chose to lie) or you can just quit out to the menu. Once you are back at the menu for the case, pressing Shift+L+4 on PC or 
+
+
+
and selecting Mystery Solved on console will load you back in to where you have to make the choice, so you can just select the other so you don't have to play through the whole case a second time.
And that's two cases down, one more to go!
Case 3 - Corruption at Cowboy County
Someone has stolen all of the hats at Cowboy Country and it's up to you and Lobster Cop (mostly you) to solve the case!
To start with, Mary from the last case will give you a refresher of the previous case. As with the other cases, answer the phone when it rings and Mary will be playing the part of both Frog Detective and the Supervisor. When the call ends, pick up the magnifying glass and open the door. You'll get some more information from Mary. After a short cutscene of the Frog Detective arriving, look to your left and you'll see a yellow phone booth with a scooter next to it. Answer the phone when it rings and the supervisor will tell you that the scooter is for you. Interact with the scooter, you can use this to move around faster with 
/left shift.
Follow the path to the right and you'll be greeted with an opening sequence. Once this is over, make your way towards the town and speak with Lobster Cop, you should earn:
You'll meet Sheriff Mason Mole during your conversation with Lobster Cop. He'll give you your notebook which you foolishly left behind, and Lobster Cop will instruct you to get a map, a tool, a key, and a meal for Lobster Cop.
Once you regain control, we'll get a couple of missable achievements. Firstly, we'll hop on our scooter and head towards the graveyard at the back. I found this achievement to be quite picky, but we are going to attempt to jump into the graveyard (it isn't actually possible). I found success going around to the left side of the graveyard and jumping from the side of it, just keep it up and eventually you'll get:
Next up, head into the salon (first building on the right, when facing away from the graveyard) and speak with Bonnie at the counter. Select both of the options to be able to interact with the pictures on the wall. To get Bonnie's quest started, she needs a carrot and four cactus Flowers. When you have finished speaking with Bonnie, interact with all of the pictures on the wall and a mysterious ghostly image will suddenly appear in an empty space. Grab this and speak with Pistol near the entrance to the saloon. Select the A muse... option, and then Give item (ghost pic) to earn:
We're done with missables for now, so head up the stairs and speak with Dusty on the balcony. He'll ask for your help constructing the perfect poem. It doesn't matter how you construct the poem, he'll be happy regardless and give you some writing supplies.
Once you are done with Dusty, head out of the saloon and carry on along the same side into the shop. Interact with the carrots on the table on the right, then speak with Wendy at the counter. She wants a portrait of herself to match the others in the shop, she'll give you a photo which you can go and give to Pistol back at the saloon. He'll paint a portrait of her, which you can give to Wendy for a ladder.
Carrying on along this same side, you'll find Craig in the post office, select the The Ghost Spotters League... He'll ask for a photo of a ghost from the saloon, which we already have, so select Give item (ghost pic) and you'll get a pickaxe.
Opposite from Craig you'll find Susy, who you'll have to speak with twice because you flaked on your promise (rude!). After speaking for the second time, select the The vault... option and she'll ask for you to get her a fake ID so she can get into the vault and get you the map you need.
Moving onto the next building, just take the gloves from the desk. You'll need these to get the cactus flowers for Bonnie. now speak with Rhonda Dynamite in front of the barn, select the About being the sheriff... option and Rhonda will ask for writing supplies, select the Give item (writing supplies) option and finally select Fake ID for Susy... Now you have the ID go back to Susy, select Give item (fake ID) and you'll get the map.
Now look to the entrance to the town and you'll find a cactus on the left side with a flower on it (Flower 1/4). Turn around and make your way back towards the graveyard and to the left of the gate there will be the next flower (Flower 2/4). Carry on up the hill on the left side and halfway up will be another flower (Flower 3/4). At the top of the hill you'll find Sherman, select The mine... option and Sherman will tell you he wants to get into the mine because there's gold in there. Select Give item (pickaxe) and you'll get a shovel.
Turn around and head to the other side of the graveyard, follow the path around and you'll find a well. Interact with it and you'll be able to climb down using the ladder, grab the key from the well and interact with the ladder to climb back out. Continue from the well and up the hill. At the end of this upper area will be the last flower (Flower 4/4). Now go back to Bonnie at the saloon and select Give item (carrots) and Give item (cactus flowers) options and you'll get the stew.
Finally we have all the items for Lobster Cop, so go speak with him. Select the I think so! option and he'll tell you to go on ahead, so interact with the locked gate, go around the back of the church and interact with the dirt pile, and you'll have found the hats! Go back to the town and you'll find everyone gathered around, after a cutscene where Frog Detective is framed for the crime, you'll unlock:
Then, after some credits and more cutscenes, you'll regain control (but as Mystery Monkey) and unlock:
MONKEYNew playable character unlocked.
Enter Frog Detective's office and interact with the clue detecting powder on the desk. Turn around and use the powder on the portraits of Frog Detective, Lobster Cop, and the Supervisor to uncover the kiss marks, unlocking:
KISSFind some secret kisses.
That's the full 1000G, so congratulations! I will be finishing the guide off, as there isn't much left to go. If all you wanted was the 1000G, then this is goodbye from me and I hope the guide was useful for you!
Moving on from the portraits, you can use the clue powder on the floor to find footprints that lead into Lobster Cop's office, follow the clue trail to the desk drawer and interact with it.
After the cutscene, you'll be back at Cowboy County. Go to the barn you found Rhonda at earlier and speak with the outlaws. Now you can turn around, enter the Sherriff's office and speak with Frog Detective. This will initiate the final cutscene.