The Plato Colony is the first permanently manned moonbase, but it could be the last. Budgetary restrictions mean the base is to be abandoned in seven days, but while the colonists prepare to evacuate, chief administrator Malcolm Wade faces other, more troubling problems.

A mysterious anomaly has appeared outside the base and an unknown assailant is attacking the colonists. As only seven people live on the moon, Malcolm reckons he should be able to find the culprit, but with the anomaly getting closer every day and with the attacks growing in severity, he suffers premonitions of an impending disaster.

With time running out to save everyone can Malcolm work out who, or what, is to blame?