Mannequin stars Joan Crawford as Jessie Cassidy, a girl of the tenements (though this being an MGM film, her slum dwellings are cleaner and more lavish than most middle-class bungalows!) Hoping to escape her grimy surroundings, Jessie marries Eddie Miller (Alan Curtis), a childhood acquaintance who has made good with a variety of dishonest business ventures. Another refugee from Jessie's neighborhood is John Hennessy (Spencer Tracy), who has likewise worked his way up to fame and fortune, albeit more honestly than Eddie. Faced with mounting debts, Eddie callously orders Jessie to divorce him and marry John for his money -- then divorce John and return to Eddie with the cash. Jessie reluctantly goes along with the scheme, but she double-crosses Eddie upon falling in love with John. Things look bad for our heroine when Eddie, with blackmail on his mind, threatens to spill the beans to John about their little "arrangement" -- whereupon John solves the dilemma (and saves his marriage) by losing his own fortune.
~ Hal Erickson, All Movie Guide