SG-1 are on the planet designated P4x-639 observing a very active sun. Daniel is with an alien archeologist, Malakai and is studying the writings on the walls. As some storms become more violent Malakai is very eager for Daniel to leave, as Daniel isn't leaving yet he shoots him and starts to operate a machine. As the geomagnetic storms increase some energy starts building up around some columns and fires itself at the gate which dials Earth. On Earth the stargate is covered in electrical energy. As the other members of SG-1 approach they notice Daniel unconscious and Malakai fiddling with the machine, Jack and Teal'c grab Malakai but as they struggle with him all three are hit with a blast of energy. The next second Jack is back at the SGC eating fruit hoops and is in the middle of a conversation with Daniel and Sam.

Electrical energy builds up around the gate on 639.

All the members of SG-1 go to briefing Sam is carrying out, the briefing is about the visit to P4X-639. Jack and Teal'c know about the mission even though everyone else says they haven't been on it yet. Suddenly the gate dials up, SG-12 arrive back with an injured man, Jack and Teal'c guess this was what would come through the gate. Jack and Teal'c are given an examination by Dr Frasier as Daniel asks them about what happened on 639. Dr Frasier reports they are in perfect health.

Frasier examines Jack and Teal'c.

General Hammond orders the mission postponed. In a corridor Daniel stops Jack and talks to him about the writings on the wall, there are over 400 pages of text, as he is explaining it Siler comes running out of the side corridor and straight into him. Sam and Jack now talk, she thinks the gate is responsible for sending them back in time, just as it sent them to 1969. In Hammond's office Jack and Teal'c are given the all clear just as the gate starts dialling up, electrical energy arcs over its surface and Jack finds himself back eating cereal.

In the briefing for the mission to 639 Jack and Teal'c start explaining everything again. Again Dr Frasier examines them and Jack and Daniel talk, as Daniel tells him that the writing are by the Ancients Siler bumps into him. Hammond agrees to let them go back to 639 where they meet Malakai. As Jack goes through his stuff the alien device starts to activate and does what it did before. Just before they get sent back to the start of the day, Malakai makes a mistake revealing he is also in the loop, but he wants to be.

SG-1 confront Malakai.

Back in the briefing Jack and Teal'c explain everything again and say there is no bother having old Doc Frasier examine them, but she does anyway. Sam and Hammond talk, Sam is inclined to believe them as Jack was using the correct technical terms for what is going on, something that is very unusual! Jack and Teal'c go to see Daniel and tell him to concentrate on the text on the alien device. Sam calls a briefing and explains that she thinks that if they dial out they will break the loop as 639 won't be able to dial in. At the correct time they try to dial out but the 7th chevron will not lock, 639 dials in and the loop restarts.

Jack again goes to see Daniel and tells him to de cypher the alien device, Daniel says he can't possible do it in a day, but Jack has thought of that and pulls out a tape recorder, but it is blank, for obvious reasons. Daniel says that if he is to do it then Jack and Teal'c will have to help him and remember what he has deciphered each time the loop restarts.

Jack and Teal'c help out Daniel.

Sam and Hammond talk, she tells him that Jack told her that they tried to dial out in the last loop but couldn't. She has done some investigating and has found out that Earth is connected to a number of planets with 639 at the centre. As it stands they can only be dialled from or dial to one of those planets, luckily for SG-12 one of those planets is the one they are on.

Jack and Teal'c are helping Daniel as the loop repeats itself over and over. In one of the loops Daniel asks if they have been doing stuff that they shouldn't as they wouldn't have to worry about the consequences, Jack suddenly perks up and even Teal'c gets a little glimmer in his eye! As the loops progress we see Jack making clay pots and cycling threw the base. Teal'c pushes a man back threw a door that he keeps slamming into his face every time the loop restarts and they both play golf threw the gate, Jack also resigns his commission and kisses Sam in the control room.

Jack and Teal'c get up to crazy stuff.

Having finally completed the translation we find out that 639 used to be a colony of the ancients and that they built the time machine to help avoid a looming disaster, unfortunately it didn't work and kept sending their scientists round in a loop, they eventually gave up and faced the disaster. Returning to 639 they face Malakai who has blocked off the machine with a modified Goa'uld forcesheild, he will not allow them to break the loop. Malakai explains that his wife died and that he wants to master the machine so he can go back in time to be with her. After telling Malakai that the device doesn't work and that he also has 14 other worlds trapped in a time loop Jack tells him about the death of his son and says that he would do anything to be with him again but certainly couldn't live through seeing him kill himself again and asks Malakai if he could live through seeing his wife die again, he says he couldn't and turns off the machine.

Back at the SGC we find out that Earth has been cut off from the outside universe for at least 3 months as the Tok'ra have been trying to contact them for that long. Daniel asks Jack if he was tempted to do anything he shouldn't, Jack just smiles at him and continues eating his oatmeal.