Hoshi and Trip return from an away mission on a planet when Trip starts complaining of feeling ill. Hoshi becomes sick soon after so Archer confines them to quarantine until they find a cure. During investigations, Phlox discovers that the virus is silicon based not carbon based which most human viruses are. The virus is not natural to the planet, it has come from another world on the back of a meteorite. Throughout the whole of the episode, Malcolm and Mayweather act strangely as though they are observing what is going on. The infection takes hold over the two crew members , Hoshi and Trip with the rest of the team unable to do anything. Whilst in quarantine , Hoshi is able to escape despite the security surrounding their place. Trip manages to capture her and bring her back into the isolation tube. With no other option, Phlox and Archer take the two sick people to the medical bay to try ionising the body therefore eradicating the virus. Once Archer is alone with the infected, the infected come to live. They reveal, the bodies have been taken over by Algarians and are being used to study the alien life they encounter. Archer manages to persuade the aliens to leave the bodies which he succeeds. Malcolm and Mayweather would seem to be infected but are not cured by the end of the episode. You may find this similar in a way to the Andromeda Series 2 episodes 'Dance of the Mayflies'.