The second trailer for The Hangover Part III was released yesterday, and it clears up some of the mystery regarding the film's plot.  

Zack Galifianakis' character, Alan, has lost his father and he's stopped taking his medication.  The other guys in the wolfpack try to convince him to go to rehab.   Based on this trailer, I'm not expecting fans of the first two movies in this franchise to be disappointed in The Hangover Part III.   It opens on May 24th.

Hollywood Life