Outwardly alien arrivals from a distant sea, the lambdas are genetically human. They slip quietly into low- to middle-income jobs and appear to want nothing more than to be left alone. For Cara Gray, they are first a haunting presence in her otherwise ordinary childhood, then the inscrutable target of her police surveillance work.

When a bomb goes off at a school, a nebulous group of lambda extremists claims responsibility for the attack-but how could a vulnerable community of tiny aquatic humans, barely visible in society and seemingly indifferent to their own exploitation, be capable of something so horrific?

In Cara's world a toothbrush can be legally alive, a quantum computer has the power to decide who dies, and a government employee made of slime mould protein needs help to relieve his neuroses. As Cara's relationship with the lambdas deepens, she must decide whether to accept her place in a pattern of technology, violence and deceit, or to take action of her own.