The Shield is Earth's only defence. Rendering the planet invisible from space, it keeps humanity safe - and hidden. The exceptional minds of the Actives maintain the Shield; without them it cannot function.

When an Active called Tobe finds himself caught up in a probability loop, the Shield is compromised. Soon, Tobe's malady spreads among the Actives and Earth becomes vulnerable for the first time in a generation.

Tobe's assistant, Metoo, is only interested in his wellbeing. Earth security's paramount concern is the preservation of the Shield. As Metoo strives to prevent Tobe's masters from undermining his fragile equilibrium, humanity is left dangerously exposed...