The Spy

 is an episode of the series from its first and only season.

Characters

 * Laurie
 * Gordon
 * Drew
 * Swinton
 * Nimbar
 * Gorganus
 * Isolus

Plot
A foreign exchange student named Ilse turns out to be the evil alien Isolus, sent by Gorganus to discover the Sentinels' identities.