"It's a Boy" stars Horton as Dudley Leake, who is betrothed to Mary Bogle (the very pretty Wendy Barrie). Shortly before the wedding, Dudley blurts a confession to his friend and best man, Jim Skippett: 20 years ago, Dudley had a brief affair with a certain Miss Piper, but he's never heard from her since then. Next day, who should suddenly appear? A youth about 19 or 20 years old, claiming to be named Joe Piper. Is he Horton's son, or is Skippett playing a practical joke?