You get this in Act 1 when you take the movie reel to the cinema.
When you see the movie screen, head down stairs and you'll see three guys appear on screen.
Didi (the little girl) tells you to put in the movie reel to stop the fight. DON'T.
Just wait and you'll be 15GS richer.
EDIT: Per comment from Premoz (thanks!), if you miss this, just go to chapter select and select "The usual suspects."