Earth Colony 150, EC150, lies at the limits of the territory of the Earth Confederacy, is a mining colony. Suddenly, shipments of ore cease and communications fell silent. An alien insect predatory life form, with telepathic abilities, has invaded. The race is dubbed the Siren bugs because they lure their prey by telepathic signals far out into space. The signals draw several space freighters to their doom.

Admiral Akiyoshi fears that the Siren Queen may gain control of an Earth Force warship and force the crew to fly her to Earth where the population would be doomed.

Jim Stewart realizes that only The Watchers can save them from enslavement to the powerful Sirens and he appeals to the Council for help. They agree to help but he has to pay an awful price to save Earth.