"Double Cross My Heart" is the thirty-eighth episode of the TV-series Danny Phantom. A new goth from Hungary captures Sam's eyes - and heart. Danny however suspects he's with the Guys in White, or is he merely just jealous?
Skulker hunts a small, menacing ghost only to be captured by the Guys in White in the process. Skulker exits his robotic body suit in time. The Guys in White immediately analyze the suit to find information on Danny Phantom.
The next day inside the Nasty Burger, Tucker and especially Sam complain about Danny's still budding romance with Valerie, whom he stares at lovingly as she works, saddened that he still can't date her. Sam complains further on the prospect of romance, stating she wouldn't be caught dead eyeing someone lovingly like Danny did.
However, she is quick to shift perspective when she eyes a tall white haired boy with dark clothes and sunglasses entering with Mr. Lancer. Lancer introduces the boy as Gregor, a foreign exchange student from Hungary. Immediately he and Sam connect, seeing they share many common traits while Danny watches, annoyed.
His Ghost Sense lets out afterwards. He and Tucker go off to fight ghosts, only for Danny to immediately run into the Guys in White. Sam and Gregor continue eyeing each other despite the chaos outside. The Guys in White and Danny both put up a decent fight, eventually with Danny coming as the victor. He then flies over to where Gregor is walking with Sam and Tucker (the latter also warming up to him due to their similar interest in technology), again to Danny's irritation. Meanwhile, the Guys in White (residing in a motel) discuss the primary locations of Danny Phantom.
Back in school, Danny confesses to Tucker that he doesn't trust Gregor despite his friend's protest to give him a chance. Gregor appears from behind, compliments Danny, then leaves with Sam to get a tour of the school. Another ghost appears (an ectopus) and again Danny is confronted by the Guys in White, this time inside the school swimming pool. Luckily Danny is able to escape when they use a device only meant for deep water use, causing the pool to explode.
In an alley later that night Danny speaks with Tucker, stating that he thinks Gregor is part of the Guys in White, seeing as he appears at the same time they do. As such he decides to spy on both Sam and Gregor, something Tucker is livid towards. Danny spies on them while the two date, eventually ending up in Amity Park Mall where the Guys in White pursue him once more. He asks why the two are after him to which they merely reply he's a ghost that "operates freely."
Desperate, Danny flies to the mall parking lot and hides there until they leave only to face Sam and Gregor leave the mall as well. There, Gregor kisses Sam, much to Danny's shock and dismay. Danny silently flies off before Sam states to Gregor she wants to take things slow, which he says he respects.
By school the next day Danny lets Sam know he spied on the two, much to her anger; she storms off with Gregor when he comes by. Tucker volunteers to spy on Sam and Gregor for Danny. After he leaves, Danny spots the Guys in White talking to Lancer where they convince the teacher to give them the information they need. Danny decides to lay low and let Tucker do his spying for the time after witnessing that scene. Tucker, as a result, continuously interrupts any romantic time Sam wants to spend with Gregor while the latter seems to appreciate his company. When Danny calls to check up on how Tucker is doing, it is plainly obvious even Tucker is enjoying Gregor's company more than spying.
Danny, inside the boys' locker room the next day, tries to think of a way to speak with Gregor about his concern with his involvement with Sam. Gregor comes up to Danny instead and already lets him know he noticed that Danny doesn't enjoy his company, if not to protect Sam. Then he asks him if he likes her to which Danny hesitates. Seeing that as a sign of insecurity Gregor tells Danny he will ask her out, then leaves, causing Danny even more emotional confusion.
It gets worse when he walks home to see his family being questioned by the Guys in White on their possible involvement with Danny Phantom. Figuring that Danny Fenton is not the ghost boy they're looking for (declaring him too prepubescent), the Guys in White list down various suspects until they believe Gregor to be the ghost child. Recognizing that Gregor, Sam, and Tucker are in trouble, Danny goes looking for them.
Atop a building located on a high cliff, Tucker eyes the stars through a telescope while Gregor wishes to have a word with Sam alone. He asks to go steady with Sam to which she is about to agree with until Tucker comes to annoy them further and finds out he's instead a boy named Elliot from Michigan who was merely acting that way to cause Sam to be attracted to him. Upset, she breaks up with him, leaving Elliot to flirt with other girls nearby.
However, it is short-lived when the Guys in White, from their jet plane, send a missile his way. Danny flies over to try and subdue them while Gregor avoids more attacks, even going as far as being rescued by Tucker. Danny manages to get inside the jet plane, lift the Guys in White out of their vehicle, then throw them into the mud below, threatening them to leave the kids alone before flying off. The two are then faced with their leader who disapproves of their dirty suits.
At school the next day Danny apologizes for spying on Sam, who states that she and Gregor/Elliot are over, saddened that her former love interest was a complete fake. Danny cheers her up by complimenting her, stopping just short of the word "pretty," causing her to blush. Danny and Sam rekindle their friendship while Tucker uses methods Gregor/Elliot used to try and score with Paulina and Star, only for them to slap him.
- While Tucker is "spying" on Gregor and Sam he tells them a story and from what the audience hears of it, his fly was down the whole time. This is a reference to the episode "Doctor's Disorders." When the disembodied head of Jazz Fenton is caught by Tucker, she comments that his fly is open, with Tucker having caught her with her head facing his fly.
- When the Guys in White are talking to Mr. Lancer outside of Casper High, they mention information about a purple-back gorilla tracing back to an assignment Lancer gave, a reference to Danny's extra-credit research assignment on the gorilla in "One of a Kind."
- Danny spying Sam and Gregor was also did the same thing on Jazz and Johnny 13 in 13 making him suspicious and not trusting him since she fell for him after he saved her life from the coaster before Danny did.
- Allusions: See List of allusions
- Goofs: See List of goofs
- Incidentally, in the Hungarian dub of the episode, Gregor is supposed to be from Hamburg. Thus the "hamburger-Hamburg" word joke is used instead of "hungry-Hungary" in the Nasty Burger scene, when first meeting with Gregor.
- The use of "hamburger-Hamburg" is also used in the Spanish dub, since in Spanish, "hungry" translates to "hambre" and "Hungary" translates to "Hungría."
- This marks the first time where Danny and Sam's love roles are reversed. Usually it is Danny who does the dating while Sam is the one who is either spying on or feeling jealous of them.
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