Here’s some music-nerd fanfic: a seductive collab between Charli XCX and Carly Rae Jepsen about the narcotic allure of riding in fast cars at night. “Backseat” is the lead track off Charli’s new Pop 2 mixtape, and wisely so: Why waste time giving the people what they suddenly know they always wanted?

“Backseat” makes much of the contrast between their two voices—Charli’s robotic low register and Jepsen’s sugary-high pitch—before flinging them across octaves until they’re indistinguishable. The verses are little encapsulations of Charli and Carly’s respective familiar themes—midnight parties and fleeting fame, then cutting right to every feeling of sadness and bliss at its most intense. But they share a certain alienation in common, the sort that can only be soothed alone with the radio. Producer A. G. Cook’s arrangement gets out of their way until the end, when he adds a burst of sparkly synth arpeggiation and low bass shudders, crashing percussion, and their two vocals, newly chopped-up and processed past humanity, blissfully lost in the mix. Pop 2 is a virtual who’s-who of alt-pop in 2017 but, even among such great company, Charli saved the best for first.