What Became of Jack and Jill?

What Became of Jack and Jill? is a 1972 British horror movie.

Johnnie Tallent is a callous young mod who lives with his elderly, invalid grandmother, Alice. Lazy and unmotivated, Johnnie dedicates most of his time to taking care of Alice to remain in her good graces so that he can inherit her small fortune and valuable house after she dies. What free time he has, Johnnie spends with his girlfriend Jill Standish, an even more callous travel agent.

Jill encourages Johnnie to take active measures to accelerate his grandmother's death, so that the two of them can get married and retire on Alice's fortune. Together, the two concoct a plan to induce a heart attack in Alice by gaslighting her, effectively murdering her yet leaving no evidence of the crime. To this end, Johnnie slowly begins convincing Alice that London's twenty-somethings, feeling that the elderly have become a drain on society, are planning a youth revolution, with the goal of either killing the elderly or placing them in internment camps. Johnnie manipulates Alice's access to newspapers and television, using stories and footage of protests to further convince her that the youth revolution is growing and becoming progressively more violent.

To further enhance his story, Johnnie and Jill cover the wall outside Alice's bedroom window with ageist graffiti. After several weeks, Alice grows paranoid and reclusive, and her health seriously deteriorates. Finally, Jill uses her position at the travel agency to schedule a large parade to pass by Alice's house one afternoon; that morning, Johnnie tells her that the revolution has begun, and that rioters are going door-to-door looking for elderly people to kill or inter. When the parade arrives, Alice, already in a panic, suffers a heart attack. Johnnie allows her to die before calling an ambulance.

At the office of Alice's probate attorney, Johnnie and Jill learn that she placed a codicil in her will that, as long as he remains in a relationship with Jill, Johnnie is only allowed to inherit her house. If he wishes to inherit any of her money, he must sever all ties with Jill and marry another woman. Johnnie and Jill initially attempt to find well-paying jobs of their own in order to keep the house, but neither are willing to work hard, and eventually their electricity, gas, and water are all turned off. The pair concoct a plan for Johnnie to date and marry an impressionable young woman in quick succession, allowing Johnnie to collect his inheritance; he can then end the relationship and be with Jill. However, Jill becomes violently jealous when Johnnie appears to develop feelings for their target, and the two get into a physical altercation. Johnnie accidentally stabs Jill in the abdomen, and she stumbles out into the street. Neighbors call the police, who arrive as a sobbing Johnnie crawls towards Alice's room, screaming for his grandmother.