Cloaked Xyrillian ship that secretly fed on Enterprise's plasma wake in Unexpected, where Trip Tucker's visit aboard left him unexpectedly pregnant.
The Xyrillian ship was discovered hidden in Enterprise's wake in Unexpected, cloaked and drawing on the plasma exhaust to recharge its failing engines. Its captain apologised, and Archer offered help, sending Trip Tucker aboard for three days to make repairs in its strange alien environment.
There Tucker grew close to the engineer Ah'len, who shared her thoughts with him through a seemingly harmless holodeck game. Back on Enterprise he discovered he was carrying a Xyrillian embryo, and Archer had to find the cloaked ship again, with help from a Klingon commander.