Amy Adams plays the cult-leader's wife, looking a lot like Princess Leia from Star Wars. I also picked up on this acronym and figured it was Scientology jargon for becoming an unperson or being carted off for re-education. We're told 'It's not about Scientology' but The Master is clearly inspired by the cult.
At its core, this is a film about charismatic, manipulative cult leader Lancaster Dodd (played by Philip Seymour Hoffman) who takes a shine to psychologically damaged seaman Freddie Quell (Joaquin Phoenix) and brings him into 'The Cause' where he attempts to 'deprogram' him.
Dodd is a smart top-of-the-range psychopath (he charms, fabricates and lies - holding back violence and naked aggression as a last resort); Freddie Quell is a bottom-of-the-range psychopath: stupid, inarticulate, poor impulse control, violent and odd. Their relationship is part utilitarian (it's convenient for Dodd to have a violent enforcer), part filial (there's a father-son relationship in there somewhere) and part homoerotic (they have a tendency to roll-around together in a manly kind of way, and they get a bit misty-eyed towards the end).
The film impresses for the sheer acting quality of its main stars and the depth of its analysis of cult-dynamics. I was wowed but was asked to mention here Clare's opinion that the main characters were deeply unlikeable and unsympathetic, which could lead the viewer to feel under-engaged with the film (but not me!).