Ensign Hoshi Sato passes through the transporter and finds that she is disappearing. At the same time, she is the only person who can see aliens planting explosives in key ship systems, with no way to warn the crew.
Ensign Sato and Commander Tucker are on an away mission, taking pictures and gathering data and samples from an ancient set of ruins. Their mission is cut short, however, when a diamagnetic storm approaches, but before they can make it back to the shuttlepod they are forced to use the transporter instead. Sato is reluctant to use it, so Tucker goes back first. After the incident, aboard Enterprise, Sato feels that things are not right, particularly being the first time she used a transporter. After a visit to Doctor Phlox, she goes to sleep, hoping to feel better in the morning.
She is wakened by an emergency call from the bridge having apparently overslept by three hours. On the bridge, Captain Archer informs her that Tucker and Ensign Mayweather have been taken hostage on the planet while retrieving the shuttlepod. Sato is unable to help, failing to understand the "simple bi-modal syntax" of the aliens. She is ordered to return to her quarters, where she sees her reflection in the mirror fade away and water passing through her hands when she takes a shower. Phlox still cannot find anything wrong, attributing Sato's experience to transporter anxiety. But only a little while later, she completely dematerialises.
The crew begin to search for her, and she observes Phlox and Tucker scanning the ship for her residue. She watches Archer speak with her father to inform him of her "death". In her wanderings, she hears and later encounters two strange aliens who are planting and arming suspicious devices throughout the ship. Unable to warn anyone, she endeavours to interrupt the devices. This eventually leads her to onto an alien transporting device - which mysteriously takes her back to her initial away team return in the transporting room. She is disoriented, and concerned about the aliens, but Lieutenant Reed explains to her that she has been trapped for 8.3 seconds in the pattern buffer because of the storm, and that her recent experiences were only hallucinations.