Category:Cast

Main

 * Alex Lawther as James, a 17-year-old who believes he is a psychopath; the disturbed love interest of Alyssa.[1] Jack Veal portrays a young James.
 * Jessica Barden as Alyssa, a rebellious teenage girl. Initially James' intended victim but later his love interest.[1] Holly Beechey portrays a young Alyssa.
 * Gemma Whelan as DC Eunice Noon, Darego's police partner.
 * Wunmi Mosaku as DC Teri Darego, Noon's stern police partner.
 * Steve Oram as Phil, James' caring father.
 * Christine Bottomley as Gwen, Alyssa's mother.
 * Navin Chowdhry as Tony, Alyssa's abusive stepfather.
 * Barry Ward as Leslie Foley, Alyssa's estranged drug-dealing father.

Guest

 * Kierston Wareing as Debbie, Leslie's ex-girlfriend with whom he has a child.
 * Geoff Bell as Martin, a family man and creep who gives Alyssa and James a ride.
 * Alex Sawyer as Topher, a young man Alyssa meets and attempts to engage in sexual activity with.
 * Jonathan Aris as Dr. Clive Koch, an author, professor, serial killer and James' first human victim.
 * Eileen Davies as Flora, Clive's mother.
 * Earl Cave as Frodo, a miserable petrol station employee.
 * Felicity Montagu as the manager of the petrol station.
 * Alex Beckett as Jonno, one of Leslie's buyers.
 * Leon Annor as Emil, an imposing store security guard whom Alyssa is caught by.
 * Matt King as DC Eddie Onslow.
 * Kelly Harrison as James' dead mother.
 * Zerina Imsirovic as Alyssa's baby-stepsister.