Plot hole: When Iris Henderson and her two friends arrive at the hotel, Iris orders dinner and asks that it be sent up to "our" room. The waiter arrives when the three are changing. But later, when it's time for bed, Iris says good night to her friends, who leave her alone in the room (as she must be for the sake of subsequent developments).
Plot hole: Margaret tells her lover Eric that her husband thinks she's "cruising with Mother." Afterwards, when the villains are closing in for the kill, she tells the others, "It's funny: I told my husband when I left him that I wouldn't see him again" - hardly the sort of thing you tell your spouse after telling him a story to cover up your infidelity.