The Confederation is an assembly of aliens from across the galaxy. They visit worlds for scientific purposes: to discover what life is capable of creating, despite difficult environments. Many of the life forms discovered have joined the Confederation, but this is not the case for the Xenoydes.

The Xenoyds are an insectoid species whose larvae grow endoparasitically, eating their hosts until they are sufficiently weakened, at which point they finish them off and feed on them. However, there is a way to survive: passing the parasite on to someone else.

The Confederation sent a reconnaissance ship to the Xenoyds’ planet to establish contact, but the mission was a complete fiasco. Only four survivors managed to leave the planet. However, a fifth passenger invited himself onto the ship, and the only way to get rid of him is to kill his current host...