Summary: Dismayed to find Samantha hard at work painting the house, Aunt Clara conjures up a top painter - Leonardo Da Vinci. Samantha asks her to send him back but Aunt Clara can't remember the reverse spell. To make Leonardo less conspicuous, Aunt Clara zaps him into one of Darrin's suits. At his office, Darrin finds himself in Renaissance attire, with palette and paint brush. J.P. Pritchfield of Mint-Brite Toothpaste, thinks Darrin plans to use the Mona Lisa smile in his ad campaign. Darrin makes has way home and learns that Leonardo has left the house. Worried that he will be picked up, Samantha and Darrin begin a search. In a museum, Leonardo sees some modern sculpture. He thinks it is raw stone and begins to chip away with mallet and chisel. Samantha arrives in time to stop his arrest and returns the piece to its modern form.
Leonardo is wrathful that his Mona Lisa will be used to sell toothpaste. Samantha tells him the only way to prevent it is to provide another idea for the advertising. Later, Darrin presents a palette of tooth paste in matching flavors, with Leonardo's picture on the package. Pritchfield is sold on this major breakthrough into the children's toothpaste market. Aunt Clara finds the reverse spell but insists that Leonardo must paint her portrait before she returns him to his place in history.