[[quoteright:350:https://static.tvtropes.org/pmwiki/pub/images/the_hidden_enemy.jpg]]
->''Truth enlightens the mind, but won't always bring happiness to your heart.''

When Anakin and Obi-Wan's forces are ambushed during a battle to liberate the planet of Christophsis from a Separatist siege, the two Jedi discover evidence of a traitor within the Republic ranks. Anakin and Obi-Wan, suspecting the Sith, head off to Separatist headquarters and confront the assassin Asajj Ventress while, back at base, Cody and Rex uncover information that points to a spy amongst them.

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!!Tropes:

* AirVentPassageway: Slick hides in the air vents to try and escape. Rex and Cody aren't deceived, though, especially since Slick left visible footprints that show where he climbed up.
* AnachronicOrder: This episode chronologically takes place between "[[Recap/StarWarsTheCloneWarsS2E16CatAndMouse Cat and Mouse]]" (2:16) and the [[Recap/StarWarsTheCloneWarsMovie pilot movie]].
* BatmanGambit: Cody and Rex figure out Slick's escape plan. Knowing that Slick is hiding in an air vent, they lure him into their trap.
* BluffTheEavesdropper: After Rex silently points out the footprints indicating where Slick is hiding to Cody, they loudly discuss that Slick has apparently gone to the south exit, and Rex is apparently going to go there and look for him to lure him out so they can capture him.
* CallForward:
** Did you ever wonder why the Republic forces don't have any tanks or gunships in the [[Recap/StarWarsTheCloneWarsMovie pilot movie]]'s opening battle? It's because Slick blew them up the night before.
** Toward the end of the episode, Ventress departs to board the ship that she will use to kidnap Jabba the Hutt's son, kicking off the plot of the pilot movie.
* TheCameo: General Loathsom (who is introduced in the [[Recap/StarWarsTheCloneWarsMovie pilot movie]]) has a brief non-speaking role.
* DramaticIrony: Slick's rant that clones are slaves and tools to be thrown away with is mostly scoffed at since as pointed out in {{Hypocrite}}, he loses his moral high ground since he kills many clones as part of his plans. However, the true mastermind of the Clone Wars, Palpatine, ''does'' intend to throw the clones away like garbage once their [[ThePurge true]] [[Film/RevengeOfTheSith purpose]] is fulfilled.
* {{Hypocrite}}: Slick claims that his actions are to free his fellow clone troopers from what is slavery in all but name, yet his actions cause the deaths of more clone troopers than what would have happened otherwise. Rex and Cody call him out on this at the end of the episode.
* INeverSaidItWasPoison: Slick accidentally outs himself as TheMole when, while trying to pin the blame on one of his men, Slick assures him that he'll get a fair trial "when the Jedi get back". It takes a few seconds for Cody to realize that Slick shouldn't even know that the Jedi have left, and when he points this out, Slick realizes the game's up.
-->'''Slick''': I really wish you hadn't noticed that, sir... [''attacks'']
* InTheHood: Ventress is shown wearing a hood when she first appears in this episode.
* ItWorksBetterWithBullets: After forming a plan with Rex in order to arrest Slick, Cody leaves a blaster on a table. Slick grabs it, only for Cody to reveal that it's unloaded.
* ISurrenderSuckers: When Obi-Wan demands Ventress to surrender, she meekly replies "I'm all yours" while sitting cross-legged on the floor. When Anakin and Obi-Wan move to seize her, she shatters the floor with her lightsabers, dropping the pair down to a lower level of the building that they're fighting in.
* TheMole: Slick is revealed to be a traitor to the Republic.
* NoodleIncident: An unusual example, due to the episode having aired before the Legends/modern canon split. Anakin and Obi-Wan have clearly encountered Ventress before, but the circumstances under which this happened weren't shown until years later when the novel ''Literature/StarWarsBrotherhood'' was released. This is because, when the cartoon aired, the older ''WesternAnimation/StarWarsCloneWars'' cartoon was still considered canon and had already established how and when Ventress joined the separatists and first clashed with Obi-Wan and Anakin, hence their familiarity here -- but once ''Clone Wars'' became relegated to ''Legends'', this episode remained as it was despite now lacking an official reason for the characters to know one another.
* OffWithHisHead: One of the clone troopers rips off the head of the tactical droid leading the assault at the beginning of the episode so they can get information on how the Separatists knew about the planned ambush.
* OhCrap: After a lengthy discussion in which they realize there must be a turncoat in their ranks and begin planning a way to root them out, Rex and Cody are about to leave the room when Cody realizes that someone left a comlink on... and has just heard every word they said.
* OOCIsSeriousBusiness: Clone troopers paint their armor both as personal expression and as an expression of brotherhood. You'll note that Slick is the only veteran with unpainted armor.
* ProperlyParanoid: One of Slick's men accuses him of suspicious activity, not knowing that Slick had already just given himself away by saying that the Jedi weren't back yet, because only Rex and Cody are supposed to know that part.
* StuffBlowingUp: Slick blows up all of the tanks and gunships as well as the weapons depot, with only four heavy cannons surviving.
* TrapIsTheOnlyOption: When Anakin and Obi-Wan face no opposition en route to the Separatist base, they discover that it's a trap. Of course, they speed right into it.
* TurnedAgainstTheirMasters: Slick's view of his actions. He's part of a slave army bred to fight and die in a Republic he's no part of, and he wants out.
* VillainHasAPoint: Slick isn't wrong that the clones are living beings who were created just to serve in a war and with little regard for them as people by the Kaminoans.
* ZergRush: The B1 battle droids invade the positions of Anakin, Obi-Wan, and the clone troopers at the beginning of the episode with a surprise attack and overwhelming numbers, wiping out most of the Republic forces. The episode chronologically marks the first time in ''The Clone Wars'' that the B1 battle droids have been presented as a serious threat instead of comic relief cannon fodder.
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