Holiday

Holiday is the eighteenth episode of the second season of Stargate SG-1

Plot
SG-1 comes upon what appears to be in an alien lab with many bizarre devices scattered about in the room. They soon find a palm pilot-like device with peculiar symbols on it, in no language Daniel can recognize. An old man suddenly appears whom Teal'c identifies as Ma'chello, an outlaw highly hunted by the Goa'uld. The old man, after eccentrically conversing with Daniel, tells him to take hold of a device, seemingly having no more effect than a static shock. The old man collapses and is brought through the Stargate to Earth. Soon after, Daniel starts acting strangely. He claims that he was told to go home when he wasn't, walks around asking people to teach him about local customs, and befriends a tramp named Fred.

Meanwhile, SG-1 is called to the infirmary because the "old man" knows quite a lot about Daniel. They soon realize that Daniel and Ma'chello have switched bodies. However, Daniel (in Ma'chello's body) is very ill, on the verge of death. He slips into a coma, with no apparent outlook from Dr. Frasier for recovery. Carter begs him to wake up. He does, saying, "Nice to know you don't just like me for my looks!"

Ma'chello is soon tracked down after treating Fred to a "bounteous feast" of Ice Cream Sundaes in a diner. He uses his credit card to pay, allowing the police to easily locate and arrest him. He is taken straightaway to a cell at Stargate Command and bargains with Sam to keep Daniel's young body. He offers to teach Sam how to decode his "palm-pilot," which contains coded plans for powerful anti-Goa'uld inventions, written in a code Ma'chello invented. Sam quickly declines, but takes him to meet Daniel, who Ma'chello has told Sam to consider as "a casualty of war." Daniel accuses Ma'chello saying that if he really hates the Goa'uld yet would steal another's body, then he's no better than the Goa'uld.

After returning home from Ma'chello's planet to retrieve the device, Teal'c and Jack reveal they have accidentally switched bodies. Yet, trouble soon strikes as Teal'c's body contracts an illness. This mean Jack must learn kelno'reem, a deep-state of meditation Jaffa use to heal themselves, in order to make his body whole again. After many fruitless attempts in Sam's lab to switch Jack and Teal'c back, Ma'chello divulges the fact that switching is strictly a one-way process; a unique exchange of bodies can only happen once. He offers to translate his work so Earth can use advanced technology to fight the Goa'uld. Nevertheless, Sam soon formulates a plan to play a little "musical chairs" with everyones' bodies, simply rotating their minds through the affected circle of people, instead of trying a direct exchange.

Ma'chello reluctantly agrees and expresses regret that he cannot teach Sam his code. So, Jack (in Tealc's body) switches with Ma'chello (in Daniel's body). Then Teal'c (in Jack's body) switches with Daniel (in Ma'chello's body). Then Teal'c (in Ma'chello's body) swaps with Ma'chello (in Teal'c's body). Finally, Jack (in Daniel's body) swaps with Daniel (in Jack's body). Ma'chello, finally returned to his own organic vessel, thanks Daniel "for the holiday," and passes away quietly.