The Disappearance of Alice Creed (2010)

Alice Creed (Gemma Arterton), the daughter of a wealthy family, is kidnapped for ransom by two masked men, one of whom is her boyfriend, Danny (Martin Compston). The other man is Vic (Eddie Marsan), who Danny intends to double-cross once they get the ransom. Although Alice eventually discovers that Danny is one of her abductors, they are forced to continue acting like strangers, since Vic does not know about Alice and Danny's relationship -- and would kill them both if he were to find out.