The model shows how we can find ourselves acting out the roles of Rescuer, Persecutor or Victim, and can not only act out these roles but trap other people into acting them out, too. We can also have this done to us.
The book describes the roles, and discusses how they are learnt in childhood. It goes on to discuss how people intensify the dramas (and rope in others) by switching roles. Finally, it discusses how we can spot these patterns of thought and behaviour in ourselves - and in the behaviour of others - and do something positive about it.