“Drugs,” a highlight from Charli XCX’s new mixtape Number 1 Angel, channels the eerie synths and smoky drums Rihanna used all over ANTI. The production, from AG Cook of PC Music, unites his madhouse interpretation of contemporary pop with Charli’s unerring knack for killer hooks. Since teaming up with Cook and the futurist producer SOPHIE on last year’s Vroom Vroom EP, Charli has honed a provocative edge, pushing the parameters of the mainstream. She’s aware that life in the fast lane isn’t always a dream, and on “Drugs,” she blends the lines between love and addiction, exploring the emo darkness that lurks behind her raver halo. XCX is joined by the Atlanta singer Abra, who steals the show for a few bars with her alluring coos, goading Charli to volley back her own enigmatic lyrics (“Biting on a flower/Blood like water down from my nose/It hurts but I can’t stop”). The track builds as XCX repeats “dealer” over and over voraciously before fizzled beats, stretched-out vocals, and the obligatory drop give this song all the feeling of a dirty cigarette butt landing in a glass of champagne. Like a fallen angel, Charli is perfectly sordid on “Drugs.”