In an alternate 1939, as imagined by the science fiction of the day, the gigantic city of Metropia is home to both humans and aliens, and the aliens run the show. Raymond Gunn, the last human private detective in town, scrapes a living from small cases with his alien colleague Eyera. When they are hired to keep an eye on Venus Nova, a pop star facing a career-threatening scandal, the job spirals into a murder investigation, drawing Ray into a web of corruption in a city where nothing is quite what it seems. A long-cherished project for Brad Bird, director of The Iron Giant, The Incredibles and Ratatouille, combining film noir with retro-futuristic science fiction in an animated feature aimed at audiences of all ages.

Bird first developed the idea in the 1990s, inspired in part by the B-52s' song Planet Claire. After recovering the rights from Warner Bros., he revived it at Skydance Animation in 2021, and in 2023 the production switched from hand-drawn to computer animation.