The Doctor teaches Seven of Nine about romance.
After catching Seven of Nine studying their relationship, Tom Paris and B'Elanna Torres complain, and the Doctor offers Seven a course in human courtship. She practises on holographic partners and then goes on a real date with a crewman, which ends when her Borg strength injures his arm during a dance. The Doctor, by now quietly in love with her, escorts her to a reception, but she leaves upset when she learns he made a bet with Paris about her.
In a lighter subplot, Neelix minds Tomin, an envoy from a strict culture who indulges in everything aboard and gets drunk on synthahol before his superior returns. The episode ends with Seven deciding no suitable partner exists on the ship, while the Doctor, unable to tell her how he feels, sits alone in a holographic bar and plays the Gershwin song that gives the episode its title. It is a key chapter in the Doctor and Seven's friendship.