Tony Ryder (Dean Martin) thinks that Katie Robbins (Shirley MacLaine) was the mistress of a recently deceased millionaire. On this fragile plot peg hangs the rest of All in a Night's Work. The millionaire died with a smile on his face, and Tony, who stands to inherit the dead man's publishing business, suspects that Katie, who has been left a fortune, administered the "favors" that pushed the old coot into the great beyond. Katie, wholly innocent, resents Tony's implications and gives him the brush-off. All turns out for the good when Tony realizes that he loves Katie for herself and not for her legacy. It took three writers (five, if you count the authors of the play upon which this film is based) to cook up the tickle-and-tease souffle that we've come to know as All in a Night's Work.