On the way back from earth the crew of the Daedalus finds a crewman dead on the floor. Immidiatly they find the cause being an electrical surge, but when they try to trace the surge to find it's origin, strange things starts to happen.
The battle in this episode is invisible, so the actors have it on hand to create a real fight with an unseen enemy and they pull it of very well.
So the basic idea of this episode: How destroy a virus that's intelligent and can hide in any system?
The episode reminds, as one of the characters mentions, another episode from stargate sg1. It's a good thing they mentioned it, otherwise I would trow the "rip-off"-card on this. It also happened in star trek once or twice, but what sci-fi show doesn't use something allready used be them.
Anyway, it's a good episode... watch it