When Enterprise is enveloped by a vast alien vessel filled with a species that appear only as wisps of vapor, these non-corporeal alien beings capture Enterprise and take form by invading various crew members' bodies to learn more about the humans, or so they say. In an attempt to get back control of Enterprise and to have his crew members' lost souls returned to their appropriate bodies, Archer enlists T'Pol's powers of mind control to determine what the aliens really want.
