"Bug!" is the fourteenth episode of the Sonic Underground television series. It first aired on 21 February 1999 in France and on 16 September 1999 in the United States. It was included in Volume 1 and Ready, Aim, Sonic!.
The song performed in this episode is "Never Give Up".
Manic surfs the air thermals in the sky over a large lake on a small red surfboard. He is attacked by a giant Stealthbot that rises out of the water and fires at him. Manic dodges and weaves in an attempt to escape. Sonic runs up and catches the robot's leg with a lasso, spinning it around and then smashing it to pieces against the rocks on the lake's shore. However, the robot's radio receiver is still active, and Sonic hears a message from Sleet saying that Queen Aleena has been spotted in Quadrant 10. In order to allay suspicion, Sonic imitates the Stealthbot's robotic voice and confirms his intention to search Quadrant 10, then disables the radio. Sonic then finds Manic (whose surfboard crashed into a cliff) and demands to know why he was out all alone, as it is dangerous and they should always go out in pairs. Manic just says he was surfing thermals, and Sonic says that he likes to surf thermals too (and is very good at it). They return to the van to tell Sonia about Sleet's message.
The van soon arrives in Quadrant 10, a bleak wasteland. Sonia wonders why Aleena would come to such a place. The van is being driven by Manic, who has a habit of hitting every pothole he passes, leading his siblings to complain. Pretty soon, the van needs a wheel change, and while they're stopped they are approached by a tall, leather-wearing lizard in another car. Although they are initially suspicious of him, he reveals through a secret codephrase that he is actually a local Freedom Fighter named Rudy.
Rudy hasn't seen Queen Aleena, but he says that's a good thing because he's been having problems. The previous night, while returning to his base, he saw a swarm of bright orange bugs, like bottle flies, leaving the village. Immediately afterwards, he was attacked by bis own friends, other Freedom Fighters, who tried to take him to Robotnik. He suspects the bugs were involved, and Sonic Underground agree to help him investigate.
Sonia is disgusted by the thought of bugs. She suggests that Sonic investigate the village, after which they will all attempt to go and catch one of the bugs. Manic wants to go with Sonic, but Sonic says there's no time and tells Manic to stay behind. However, once Sonic is gone, Manic decides that if Sonic can go out alone then so can he, and he flies off on his thermal surfboard to look for a bug himself.
Sonic finds the village burned down and no sign of the Freedom Fighters. However, he sees one bug, which he catches in a glass jar, joking "You're a real bug and I'm a 'swat'-bot." Elsewhere, Manic also encounters a bug, which stings him on the nose. Suddenly his eyes dilate and in a monotone voice he repeats "Must report... must report to Robotnik..." before flying away on his board.
Sonic returns to Rudy and Sonia, but there's no sign of Manic. Sonic gives Rudy the bad news about his village, then shows them the bug. They discover that it is definitely Robotnik's, as it is actually made of metal. Inside, they contain a mind control serum that makes people obey Robotnik if stung.
In Robotropolis, Sleet reports to Robotnik on the testing of their new Flybots. He explains that a full does lasts an hour, which is long enough to compel a person to come to Robotropolis to be roboticized. Sleet also says that they burned down the Freedom Fighter village on Robotnik's orders, but when Robotnik asks for an update on the search for Aleena, Sleet is forced to admit that they haven't heard from the Stealthbot, and Robotnik orders him to find it. Manic arrives at Robotropolis, completely under Robotnik's control. Robotnik develops a plan to use Manic to capture the other Freedom Fighters. They put a modified, remote-controlled Flybot into his pouch, which will administer a micro-dose of serum when activated by radio. They'll take Manic back to the desert before the effects of the serum wear off, and use him to deliver the other hedgehogs to Robotnik.
Manic returns to the group with no memory of where he's been, saying only that he chased a Flybot and it got away. The others say that they plan to use the cannons mounted on the roof of the van to shoot the bugs. That night, Manic is stung and reports in to Robotnik, revealing their location. A short while later, Sonic wakes up (Manic is back sleeping) and sees Robotnik's forces heading for them, so he drives the tank away before they arrive. Rudy says to hide the tank in a cave he knows. On the way, Manic is stung again and reports in to Robotnik, but he isn't able to tell Robotnik where the hedgehogs are going before Sonia spots him and takes the radio. They realize he has been stung and find the bug in his pouch, which Sonic destroys with his guitar medallion.
Sonic and Rudy develop a plan to destroy the bugs. They intend to use the van as bait to lead the bugs to a place Rudy knows where they can be destroyed. While Rudy drives, the hedgehog siblings sing a pop song in the back of the van, which attracts the bugs' attention. They reach an area in the middle of an electrical storm. Sonic leaves the van and flies around on Manic's thermal surfboard, luring a group of bugs into the storm where they are destroyed by a lightning strike (Sonic is also struck four times). The other bugs are blasted by the other Freedom Fighters with the van's cannons.
Rudy and the others return to the village, where everything has been burned. However, some Freedom Fighters begin to emerge from the wreckage, including a female lizard named Sheila. She explains that Swatbots burned the village, but some of them escaped. Rudy is glad to be reunited with them.
- Sonic says that the Flybots have "full metal jackets", a reference to the 1987 war film Full Metal Jacket.
- The title of this episode is a reference to Bug!, a Sega Saturn game which was getting its own DiC cartoon alongside Sonic Underground, but production was canceled for unknown reasons.