The story follows a boy called Thomas "Tom" Charper going to a cruel hospital and joining a "midnight gang" consisting of the facility's other children and staff.

Emily Bearn wrote in The Daily Telegraph, "it is a simple and touching story of children overcoming adversity with make-believe".

[1] Common Sense Media's Mary Eisenhart said, "British author David Walliams is in top form with this imaginative, poignant, often crude, and frequently hilarious tale of kids stuck in a London hospital.

... it's a heartstring-tugging, thought-provoking tale with unforgettable characters, relatable issues, and a determination to do better than the bad people in your life.

"[2] In a positive review for the School Library Journal, Caitlin Augusta stated, "Ross's numerous black-and-white illustrations mirror Walliams's lawless, uncontained revelry.