You will get this achievement for completing all 25 Basso Jobs in the City.
These are the jobs you will get from Basso:
- Sick Willy (available as soon as you end your first meeting with Basso)
- Beauty Within (available as soon as you end your first meeting with Basso)
- Medical Misery (available as soon as you end your first meeting with Basso)
- Writing Wrongs (available as soon as you end your first meeting with Basso)
- Machinations (available as soon as you end your first meeting with Basso)
- A Stroke of Madness (available after completing chapter two)
- The Disappearing Poet (available after completing chapter two)
- Taking a Fence (available after completing chapter two)
- A Lady's Bequest (available after completing chapter two)
- Watch Your Step (available after completing chapter two)
- Saving Face (available after completing chapter two)
- Carnivalesque (available after completing chapter two)
- Casing the Cargo (available after completing chapter four)
- Poor Protection (available after completing chapter four)
- Shark Bait (available after completing chapter four)
- Fit for a Queen (available after completing chapter four)
- Long Drop Full Stop (available after completing chapter five)
- The Path to Riches (available after completing chapter five)
- Eyes on the Prize (available after completing chapter five)
- Check, Mate (available after completing chapter five)
- A Grave Matter (available after completing chapter five)
- The Rule of Thumb (available after completing chapter six)
- The Tinker's Trinket (available after completing chapter six)
- The Witch of Stonemarket (available after completing chapter six)
- The Point of No Return (available after completing chapter six)
You can also wait until you have finished chapter six and then do all Basso jobs in one go (as I did). Just go to Basso, talk to him and accept all he has to offer. The jobs will appear as white dots on your map. After completing the first jobs you can go back and accept the next ones - just repeat this until you have done all 25 jobs.
Edit: As reported by scntyboy - if you plundered ealbiters cabinet the first time you entered the area the job "poor protection" will not be available from basso. BUT the game does give you credit for it.
The achievement will pop right after you've finished the last job.
If you are having troubles with any of these jobs I can recommend this link:
http://guides.gamepressure.com/thief/guide.asp?ID=24029This is a well written guide with pics which should solve your problems :)
If you prefer a video-guide you should check out the YouTube channel of "First Try Gaming".
http://www.youtube.com/playlist?list=PLslrHWn5Idtd-yvhkkEn73...All credits for the vids go to them!!!