Plagued by disturbing sexual thoughts and at the end of her rope, 24-year-old Marnie moves to London on a mission to change her life. Loose and alone in the big city, she stumbles into the lives of Shereen, Amber, and Joe.

Marnie hits a dead end when she goes to a sex addiction meeting, but she finds an unexpected kindred spirit in recovering porn addict Charlie. She grows closer to Amber and Joe after talking herself into a job opportunity at Ethel magazine.

Having learned what is wrong with her, Marnie is determined to make the most of being a single Londoner. She jumps into bed with earnest, clingy barista Benji, but it has consequences at work.

Marnie and Charlie work to pick themselves back up after hitting rock-bottom. Marnie receives help from an unexpectedly understanding Shereen, while Charlie tries to prove he's up to his old job.

Encouraged by therapy, Marnie entrusts her old friend Helen with her secrets, and brings her two worlds together at a big dinner party.

Marnie is shaken when she realises that she's pushed Shereen too far, and becomes paranoid that everyone has turned against her now they know about her condition.