Marshall and his brother grew up between their costume- and set-designer mum’s house, in south-east London’s East Dulwich district, and, on odd weekends, their dad’s more middle-class flat in nearby Peckham. “My mum wasn’t really there that much,” Marshall says, doodling on a Polaroid of himself from the photo shoot. Does he wish she had been? “Yeah... I wish I got better meals.” He laughs. “I didn’t know how to cook. We ate a lot of frozen food and takeaways.”

In other ways, life in a loose, artistic household suited him. Marshall’s mom often took him to concerts, threw wild house parties, and, in quiet moments, would dissuade him from TV in favor of art and music. He remembers writing his first songs at age 8—“the trashiest shit, singing in an American voice”—and later recording prepubescent experiments on a Roland 8-track, the machine that would consume his early adolescence.

At a pub just up the road from where he’s telling me all this, Marshall, then around 12, performed what he calls his first “good song.” Impressed, a coterie of pot-smoking, skinny-jean-wearing indie kids drew him into their orbit. Weed and music elevated him from a bored, awkward kid to a wilder entity. He was often excluded from school for, by his admission, “stupid dumb shit where I really deserved it,” usually involving drugs or graffiti. He wound up at an education center for expelled kids. “I was getting bullied,” he admits. “It was quite a weird time.” Marshall met a fellow oddball who seemed to share his interests; every lunchtime, they’d disappear off-site and smoke away their appetites.

The local government threatened to imprison his parents if he wouldn’t bend to the education system. A homeschooling experiment with his father ignited little academic passion, not least because his dad’s dawn-till-dusk hours meant Marshall would spend long days alone, burdened with books like Oliver Twist. “That shit was hard to read,” he recalls, grimacing. “Charles Dickens refers to Fagin as an old Jew for a lot of it. It’s like, Ugh, what’s going on!”

Boredom had its rewards, though. In his free time, Marshall became enshrined in musical wormholes. “It was a time when music was essentially trash,” Marshall says of the mid-2000s. “Indie, pop, the Libertines, that sort of thing. But it was quite influential on me. Albums like [Justin Timberlake and Timbaland’s] FutureSex/LoveSounds really threw my mind—the production was crazy.”

Marshall’s lifeline was the arts-minded BRIT School, where classes mixing politics, sociology, and music history coax unconventionally minded pupils into a relaxed form of education. As Marshall puts it, “I met a load of people who were soft and into similar fucking pansy music I was into.”

A major factor in Marshall’s progress was Derek Moir, a senior faculty member and onetime guitarist in postpunk outfit This Poison!, which helped prop up Scotland’s DIY scene in the 1980s. On his first day, Marshall swaggered up to Moir claiming to recognize him—and was promptly sent away. On another occasion, he walked into class with a foppish, New Romantic-style haircut. “Derek looked at me and said, ‘Why the hell have you got that haircut?’” Marshall remembers, laughing. “There was a really good connection. I hated him but I loved him. But he gave me a place to actually be romantic and be all right with it, rather than going down the same old lines.”

Moir remembers the young Marshall fondly. “He was a bit awkward and gangly and ginger but he had confidence,” he tells me, speaking by phone from the BRIT School. If Marshall sometimes lacked patience, Moir says, he made up for it by obsessing over his pet subjects. “Initially he was quite shy, but he was politically and socially aware. He wanted to grasp as much as he possibly could about the world, and you could see he was trying to fuse that with his art.”

Marshall’s three years at BRIT weren’t all rosy—he still smoked every day, and when threats of expulsion loomed, Moir was forced to speak up on his behalf. But in the end, Marshall orchestrated his own exit. At 17, partway into a music course, he abruptly switched lanes to art. “He felt he’d learned all he could in music,” Moir says. Nobody seemed to argue—by that point, Marshall’s reputation as a prodigy was cemented.