When a scientific expedition is launched to study a mysterious alien race, the only ship available is the Nightflyer, a fully autonomous vessel manned by a single human. But Captain Royd Eris remains locked away, interacting with his passengers only as a disembodied voice - or a projected hologram no more substantial than a ghost.

Yet that's not the only reason the ship seems haunted. The team's telepath, Thale Lasamer, senses another presence aboard the Nightflyer - something dangerous, volatile, and alien. Captain Eris claims to know nothing about the elusive intruder, and when someone, or something, begins killing off the expedition's members, he's unable - or unwilling - to stem the bloody tide.

Only Melantha Jhirl, a genetically enhanced outcast with greater strength, stamina, and intelligence than other humans, has a chance of solving the mystery - and stopping the malevolent being that's wiping out her shipmates.