George MacKay as Jack Marrowbone

Anya Taylor-Joy as Allie

Charlie Heaton as Billy Marrowbone

Mia Goth as Jane Marrowbone

Matthew Stagg as Sam Marrowbone

Nicola Harrison as Rose Marrowbone, Mother

Kyle Soller as Tom Porter

Tom Fisher as Simon Fairbairn, Father

Myra Kathryn Pearse as Molly

Paul Jesson as Doctor

Robert Strange as Monster

Laura Brook as Thelma (uncredited)

Adam Quintero as Mr. Gouldman (voice) (uncredited)