The Haly International Traveling Circus is performing in Bruges and its newest performers, the Danger Family, give their premier performance. The five members are Young Justice members Robin, Miss Martian, Red Arrow, Artemis, and Superboy in disguise. Robin complains that he's caught the flu and then misses a catch, and Superboy and Miss Martian secretly use their powers to knock him back into Miss Martian's grasp. As they land to take their bows, she admits that she has been using her telekinesis since she's no acrobat, but assures Robin that no one could have seen her telekinetically pull him back into her hands.
Several days earlier, Robin calls the team together and informs them that Batman wants them to look into a series of European thefts of high-tech parts. Each theft has taken place at the same time that the Haly Circus visited the city. Red Arrow offers to go along, and secretly tells Robin that he wants to find out which of the others is the mole.
As Young Justice goes backstage, the ringmaster, Jack Haly introduces the fire-breathing act as the tightrope-walking clown finishes his act. The former leading acrobats, Carlos and his brother, complain that the newcomers have been given top billing but Jack is unimpressed. Interpol agent King Faraday comes in and warns Jack that he believes someone in the circus is involved in the thefts. Jack refuses to discuss it while the show is still running and goes back into the ring. Faraday approaches the team and tells them that they're not suspects since they just joined the circus. However, he warns them that he plans to find out who at the circus is responsible and close it down when he has the thief.
Back in their trailer, Robin goes over the data and pinpoints the factory in Bruges that the thief will go after. The team gets there and Red Arrow spots the thief, a skilled acrobatic, going over the fence. As the others go ahead, Superboy uses one of Lex's patches to get his full Kryptonian powers. He then uses his x-ray vision to spot the thief and tells the others. However, when the team confronts the thief, he uses a fire-breathing trick to drive them back and set the warehouse on fire. Caught by surprise, the team realizes that there is live ammo in the building and takes cover in a cargo container just in time. By the time they can get out, the thief has already escaped. An enraged Superboy wants to go after the thief but Robin warns him that Miss Martian is weakened by the flames and needs his help. The superclone gets ahold of himself and flies his girlfriend out flames, while Red Arrow and Artemis help Robin out since he's still weakened by his case of the flu.
Back at the circus, Faraday tells Jack about the recent theft, but the ringmaster insists that he did a bed check and everyone was where they were supposed to be. The team is listening and realizes that he's lying because they know he didn't check on them, and wonder what else he's hiding. They go back to their trailer and review the security footage of the thefts. In each case, the thief displayed different skills to break in, skills that match different members of the circus. Red Arrow figures that Jack is the mastermind and sends in a different circus member for each thief, but Robin disagrees and tells them that they need to keep an open mind.
Robin storms out and Miss Martian realizes that she can scan Jack's mind and learn the truth. However, Red Arrow tells her that she can't handle it without giving herself away. Superboy thinks that he's accusing her of being the mole, having earlier overheard Red Arrow's whispered conversation with Robin. When Red Arrow points out that one of them must be the mole, Superboy prepares to attack him but Miss Martian intervenes and calms the two of them down. As she leaves with her boyfriend, Artemis tells Red Arrow that he should keep an open mind and that they're all loyal to the team.
Robin walks through the circus train cars and stops to examine a poster of the Flying Graysons. Kid Flash calls him from Mount Justice to find out why they let without him. He knows that Batman didn't give them the assignment and Robin admits that he set up the mission because Jack is an old friend of the Grayson family. Robin explains that he left Kid Flash out of the mission because he didn't want his best friend questioning his objectivity, but Kid Flash points out that's what a best friend is for.
The circus finishes its last performance and Jack tells everyone to quickly pack up so they can get to their next show in Geneva. As Miss Martian loads some luggage, one of the roustabouts, Ray, comes over and offers to help. She thanks him but says she can handle it, and the train gets underway. Robin starts feeling better but Miss Martian has come down with the same virus. However, when she tells them that it happened when Ray casually touched her later, Robin remembers Ray touching him just before he got sick. He goes out in the hall and finds Jack, who tells him that Ray joined the circus at the start of the European tour and the roustabout has the flu as well. As the team goes to find Ray, "Jack" uses Miss Martian's ability to transform into his real form of Ray.
The team checks out Ray's bunk and discovers that he's not there. They do find a crate containing ashes from the warehouse fire as well as a mask of Ray's face. The team splits up to search the train and Robin finds Jack tied up in his office. The ringmaster confirms that Ray attacked him and tied him up, and Robin is forced to use the radio to warn the others when he discovers that Miss Martian's illness is keeping her from creating a telepathic link.
Superboy finds Ray in the dining car, disguised as the circus clown and carrying a trunk. The superclone puts on another shield patch and uses his x-ray vision to confirm there's some kind of device inside. He orders Ray to surrender and the roustabout telekinetically throws tables at him and then escapes to the top of the train. Superboy flies up after him while the others arrive, and Robin says that "Ray" is actually the Parasite. He's been draining the skills of the circus performers and then Robin to commit the thefts, leaving them in a weakened flu-like condition. As he reverts to his blistered purple form, Parasite admits that he's happy that he finally was able to feed on a Martian and gain actual superpowers. He telekinetically pulls Superboy into his grasp and drains his powers, and then uses his new heat vision to destroy their bows when Red Arrow and Artemis fire at him. He starts to fly off and Robin manages to grab him, but Parasite casually knocks him aside and leaves.
When Superboy recovers, Robin wonders how the Parasite could drain Kryptonian powers from him that he doesn't have. The superclone suggests that the Parasite was able to drain his genetic potential even if he can't use it, avoiding any mention of the shields. When the others go on ahead, Superboy removes the inert shield patch and looks at the remaining ones.
The team gets into costume and Robin reveals that when he grabbed Parasite, he was able to steal the flash drive he had. He quickly decrypts it and confirms that Parasite is working for Intergang. The device in the crate is a black hole generator, and the last part can be found in Geneva. Red Arrow gets his backup bow and tells Robin that the others should stay behind because they're powerless and weaponless. Artemis disagrees, producing her own backup bow, and Superboy punches the wall to demonstrate that he has his powers back as well. When Robin wonders how he could have recovered so quickly, Superboy passes it off as his Kryptonian healing factor. Miss Martian insists on going along with them even though she hasn't recovered her powers.
When the team arrives at the science center in Geneva, they discover that Parasite has knocked out the guards and gone inside. As the others enter the building, Superboy uses another of Lex Luthor's shield patches. Inside, Parasite is wiring his device into the building's collider and activates it, creating a black hole above the building that begins pulling everything into it. Robin and the others arrive and he suggests that they scout out the situation. However, Superboy, short-tempered due to the shield's influence, charges in and attacks Parasite. The villain uses Miss Martian's telekinesis to slam Superboy around, and then grab him and drain his powers. He's surprised to discover that Superboy has recharged his powers, and then tosses him aside.
Robin and Miss Martian have a plan and he tells her to go after the villain. Using her martial arts training, Miss Martian manages to knock Parasite down, and Red Arrow opens fire with a quick-hardening foam arrow. Parasite easily breaks free and telekinetically starts to crush Red Arrow, but realizes that Robin has snuck in to shut down the collider. Artemis fires an arrow at him as Parasite uses his heat vision, and he realizes too late that the arrowhead contains flammable gas. He's surrounded by flames and Miss Martian points out that he not only has her powers but her weakness to flame. Overcome by the fire, Parasite passes out.
As Robin shuts down the collider, Faraday and his men arrive. Robin has already tipped the agent off and he has an inhibitor collar designed for Parasite. Meanwhile, Artemis helps Red Arrow up and he gratefully accepts. As the others come over, he admits that since he's seen them in action for the first time, he's satisfied that none of them are the mole and apologizes for doubting them.
Later, Robin goes to see Jack in his Danger disguise. However, the owner isn't fooled and tells Robin that he recognized a Flying Grayson by his trapeze Jack thanks him for his help and asks him for one last favor, and Robin is soon giving a final trapeze act for a cheering audience.
King Faraday first appeared in the original Danger Trail series (#1-5, 1950-51) and was created by Robert Kanigher and Carmine Infantino. He was a counter-espionage agent who worked for the U.S. government and engaged in a variety of standard spy-type capers. His Danger Trail adventures were reprinted in Showcase (May-June 1964). Faraday has since been incorporated full-bore into the DC universe as a member of the Central Bureau of Investigation. Faraday possesses no superhuman abilities but is a trained espionage agent and an expert hand-to-hand fighter and marksman.
Rudy Jones, first appeared in the comics in Action Comics #340 (August 1966). A janitor at S.T.A.R. Labs, Rudy was exposed to chemicals, and was transformed into a purple-skinned "human parasite." Since he could latch on to any superpowers, including Superman's, he became one of the Man of Steel's greatest enemies. After the Crisis on Infinite Earths, Jones' origin was somewhat updated in Fury of Firestorm #58 (April 1987) but he was still Rudy Jones, janitor turned super-villain. Since then he's fought even more superheroes and absorbed a scientist with a conscience that led to periods of a split personality between good and evil. But when he was evil, Jones could draw on the scientist's intelligence. He duplicated Lois Lane's appearance and memories and inserted himself into Superman's life (ewww...) and as of 2005 was considered dead and there seem to be at least two other Parasites running around. In the WB animated universe, the Parasite was introduced in Superman: The Animated Series, in the episode "Feeding Time." His origin is basically the same - Rudy Jones, janitor, chemical exposure. He has since appeared in other animated series.