The Chapter 3: Inheritance Add-on for Tell Me Why has 10 achievements worth 500 gamerscore.
Lock-up and leave the Ronan House with Tyler
Complete the story with the twins strongly bound together
Uncover the princess' lost treasure
Catch all the fish with Michael
Learn the truth about Sam's relationship to the twins
Help Sam fix the engine
Find out who the Mailbox Bandit really is
Start writing a new chapter with Alyson
Complete the story with the twin's bond weakened
Place all collectibles in the attic