Undercover

Undercover is the eighteenth episode of Ben 10: Alien Force.

Plot
Kevin, Gwen and Ben destroy a teleporter they were working on and need help repairing it. Kevin suggests Cooper, the young boy who had helped the Tennysons in the past. Unfortunately, Cooper has been kidnapped by the DNAliens.

They track him to Los Soledad, the abandoned military base where Paradox built his time machine. They discover that the Highbreed have erected a cloaking field, built by Cooper over the area, concealing a mysterious arch-like device. They free Cooper and have him destroy the cloaking generator, during which he has visions of the arch acting as a gateway for a fleet of ships and the Earth being destroyed. Despite destroying the generator, the Highbreed manage to repair it and continue their operations unhindered.

Major Events

 * The DNAliens kidnap Cooper for their plans.
 * Ben and the gang retrieve Cooper.

Characters

 * Ben Tennyson
 * Gwen Tennyson
 * Kevin Levin
 * Cooper Daniels (first appearance since the original series)

Villains

 * DNAliens
 * Highbreed Commander

Aliens Used

 * Swampfire
 * Goop
 * Echo Echo

Allusions

 * When Kevin said to Ben " You used to turn into one of those (insects)", he was referring to Stinkfly.
 * Ben's concerns about a "banana fly monster" in the beginning of the episode is a reference to the science-fiction horror film The Fly, the main character had a similar problem when he and a fly entered the teleporter he was working on at the same time transforming him into a fly monster.

Trivia

 * The teleporter is very similar to the Paradox's Time Machine.
 * Though Kevin shows tendencies of being protective, jealous and mad when other guys had a crush on Gwen, he was surprisingly good humoured towards Cooper for his adolescent feelings for Gwen.
 * The second hint towards the events of War of the Worlds are foreshadowed when Cooper was destroying the machine.
 * It is revealed that DNAliens cannot handle very high frequency sounds.
 * Kevin knows Cooper for unknown reasons (probably dealing with alien-weapons and advanced technology).
 * Cooper from the original Ben 10 series makes a reappearance. Apparently, he has gained a lot of weight in the last 5 years since he spent too much time in his lab.