Jack is five.
He lives in a single room with his Ma.
The room is locked.
Neither Jack nor Ma have a key.
The novel opens as Jack turns five. Jack has never been outside of Room, as he calls it, and although he and Ma have access to a TV, Jack believes that everything he sees on the screen is make-believe: as far as he’s concerned, Room is the entire world. He’s happy enough with his lot, however, because he doesn’t know any different; Ma keeps him entertained, and he has her undivided attention. Their days have a structure, with time to sleep, a time to eat, to play, to watch TV - even a time for lessons. (And at night, which is when ‘Old Nick’ sometimes visits, Ma keeps Jack hidden away.)
But now Jack is five, and Ma tries to explain to him that - contrary to everything she’s told him previously - there is a world beyond Room. Jack finds the concept impossible to grasp, but when Old Nick cuts the power supply to Room, Ma realizes their situation is even more precarious than she had previously thought. She decides they have to act, and comes up with a plan: she will tell Old Nick that Jack is dead and persuade him to dispose of the body. At an appropriate moment, Jack - still very much alive - will make a run for it.
Ma and Jack spend ages rehearsing exactly what Jack has to do, and - miraculously - their plan works: Jack manages to get out of Room, and away from Old Nick. He manages, too, to convince a bystander to alert the police, who subsequently rescue Ma.
For Jack, however, freedom is an alien concept, and he’s suddenly catapulted into a world that’s both unfamiliar and terrifying; for him, it’s escape, not being held captive, that is frightening. For Ma, too, life on the outside requires many adjustments; not least, the two have to learn how to live together in a world full of other people.