Leo (Marcello Mastroianni), the last heir of a deposed royal family, returns to his deceased father's mansion in London to find that the neighbourhood has become a slum. A recluse perplexed by other people, Leo spends most of his time in his room, watching birds and people through a spy-glass. He becomes interested in the problems of his poor, mostly black neighbours, particularly Salambo Madi (Glenna Forster-Jones), an immigrant who lives with her family, and starts leaving his mansion to try to help people. However, his entourage disapproves of his activities, especially his aide Laszlo (Vladek Sheybal), who is obsessed with trying to restore the monarchy. Leo also faces opposition from local pimp Jasper (Keefe West), who profits off of everyone else's poverty and is secretly in league with Laszlo.
Leo the Last contains examples of:
- Bystander Syndrome: While Leo is out walking, he sees Mr. Madi (Thomas Bucson) have a heart attack in the street while his son screams for help. Leo watches, frozen, until eventually some other neighbours run over to help him inside. Leo's guilt over the incident is part of what motivates him to become more active.
- Cry into Chest: Salambo cries into Leo's chest over her family's misfortunes since coming to London.
- Fan Disservice: One scene has Leo and Margaret naked in a swimming pool with some other people for some kind of health ritual. As they bounce up and down, an underwater camera shows their bodies undulating in bizarre ways.
- Gold Digger: Leo's fiancée Margaret (Billie Whitelaw) doesn't actually like Leo, but is desperate to marry him for his money.
- Gross-Up Close-Up: During a party at the mansion, rich people eat food in various disgusting ways while the camera focuses on their mouths.
- House Fire: Leo invites the neighbourhood poor into his mansion, but Laszlo, Jasper, and a small army of goons barricade themselves inside. The neighbours fire rocket launchers into the mansion, with Leo's approval.
- It's All My Fault: Leo buys food and drink for the Madis, and watches them eat through his spy-glass. But after dinner, Mr. Madi has a heart attack and dies while Leo watches. Leo blames himself for the death and has an emotional breakdown over it at his and Margaret's wedding rehearsal, to the irritation of his entourage.
- Man on Fire: Jasper runs out of the burning mansion with his jacket on fire, yelling "You're burning but you just don't know it!" until Roscoe smothers the fire with a blanket.
- Platonic Prostitution: When Salambo becomes a prostitute, Leo pays for sex with her, then begs her to let him help her. He buys her from her family and moves her into his mansion so he can save her for her boyfriend Roscoe (Calvin Lockhart), who is in jail. Salambo is very confused and wonders when they're going to have sex.
- Soft Glass: As Kowalski (Kenneth J. Warren) rapes Salambo in the room above his shop, Leo smashes the window with his sleeve and yells for help. No one hears.
- Soundtrack Dissonance: "Moonlight Sonata" plays while Leo's mansion burns.
- Trash the Set: The movie ends with Leo's flaming mansion dramatically collapsing, leaving only a heap of smouldering wreckage, which Leo contemplates during the end credits.
