The Chapter 3: Inheritance Add-on for Tell Me Why has 10 achievements worth 500 gamerscore.
Complete the story with the twin's bond weakened
Start writing a new chapter with Alyson
Complete the story with the twins strongly bound together
Lock-up and leave the Ronan House with Tyler
Uncover the princess' lost treasure
Place all collectibles in the attic
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