The opera, like the film it’s based on, is about a group of wealthy guests who assemble for a chic dinner party — and then find themselves inexplicably unable to leave, prevented by some mysterious force. The ondes, with its spooky swoops and slides and eerie timbre, represents that strange force; Mr. Adès said that it could be considered the voice of the exterminating angel.

The part was written specifically for Cynthia Millar, a leading ondes player, who will perform it at the Met. She described the sound as “very beguiling and also very terrifying.”

It will be a rare outing for an ondes in the pit of the Met, where it was used in Samuel Barber’s “Antony and Cleopatra,” which opened the new opera house at Lincoln Center half a century ago but has seldom (if ever) been heard there since. Ms. Millar said that Mr. Adès’s writing for the ondes differed from that of other composers.

“Although this is a generalization, on the whole the music that Messiaen has written for the instrument is in the character of a seraphic, superhuman soprano, wishing good to the world,” she said. “That’s not the case here.”

Rock, Paper and a Salad Bowl