Having failed his exams, Tristan fears his brother's wrath. In a desperate effort to reform, Tristan shuns cigarettes, alcohol and women and adopts a rigorous routine of dawn runs and hard work.

The mysterious Mrs. Donovan poses problems for all three partners. Siegfried rashly dismisses her as "a warm-hearted woman who loves animals" -- until she starts interfering with his patients. From sheep to piglets, a howling dog to a hibernating tortoise, there seems to be no limit to her homespun remedies. Tristan has big trouble on his hands when cadging college pal St. John turns up looking for a bed -- and a small loan. Can Tristan keep St. John's presence a secret from Siegfried and the fearsome Mrs. Alton? Lovely Rosemary Brocklehurst attracts the romantic attention of Tristan when she brings in Esmerelda, a tortoise, which won't come out of its shell. Perhaps Mrs. Donovan has the answer...