Suspecting historians seeking Marie-Antoinette's necklace, Antoine and Florence enlist his ex-fiancée Juliette, a medium cop, to infiltrate the group. Her attempt to reunite them fails as they insist on staying friends.

An art restorer is found dead in her workshop next to a Botticelli masterpiece. Florence and Antoine embark on a perilous quest leading to the Jacquemart-André museum, troubled by the Renaissance master's themes of courtly love.