Set during World War II, a twelve-year-old orphan who accidentally unleashes a shadow monster onto the streets of London must team up with unlikely allies to hunt it down.

Surviving on the streets of World War II London alone certainly hasn’t been easy, but Nimble Nottingham has perfected the art of going it alone—and that’s just how he likes it. The only friend he needs is his beloved dog, Winnie. To pass the time between rolling blackouts and bombs falling through the air, Nim spends his days fence-climbing, roof-jumping, and gargoyle-perching…that is when he’s not scrounging for food to stave off the ever-present hunger the war has brought to London.

So when opportunity strikes in the form of a bomb falling onto the notoriously creepy Gravenhurst Manor, Nim knows he has to get inside and find whatever spoils he can get his hands on to sell for food. Get in. Get out. Quick as a flash. At least, that was the plan until Mouse—a member of a local street gang called the Dead End Kids—shows up and invites himself along for the heist.

Inside, Mouse and Nim encounter far more than just crumbling walls and shattered windows. Beneath Gravenhurst Manor lies a secret room and inside that room is a locked safe. Nim, inspired by the Hardy Boys adventures he used to read at Waifs and Strays orphanage, knows that something this protected has to be valuable, and so he cracks the safe and unknowingly unleashes a monster.

A shadow creature is now loose on the streets of London, and it’s up to Nim, Mouse, and a band of unattended children to end its reign of terror.