Deanna Durbin stars as Penny Craig, the youngest of three sisters. When the handsome and debonair Richard Watkins (William Lundigan) proposes to her sister Joan, everyone in the Craig household is delighted except for Penny's other sister Kay. She was secretly in love with Richard too... Determined to help, young Penny turns to the family butler for advice. He says that Kay will forget all about Richard when she meets another 'tall, dark and handsome' man. Never one to duck a challenge, Penny finds just such a man to court her sister Kay - Harry Loren. Only Harry then falls madly in love with Joan... and everyone thinks Penny secretly loves Harry! Will the course of true love ever run smoothly in the Craig Household?