Alone. Eye of the Maelstrom, book 5

It's a sad day for the Campton kids: they've just discovered Dodzi's lifeless body at the foot of a building, shot once in the chest. Convinced that whoever killed him must have come from the red zone - the no man's land marked out by the monkeys' cairns - Leila and Ivan decide to send an expedition there. But none of the children could possibly imagine what awaits them inside the zone, no more than what will happen back at the camp.