We saw a completely different use of the flashbacks in this episode. Instead of flashing back to a point in the characters life, we actually see Desmond flashing back and forth in time.
As Frank, Sayid, and Desmond make their way to the boat, they hit some turbulence and something happens to Des. He does not know anyone on the helicopter and then he kind of passes out. When he wakes up, he is back with his platoon in the Royal Scots Regiment.
Jack questions Daniel about why it is taking so long for them to get back. Daniel tries to explain to him that time works differently on the island. Sayid calls and explains to Jack that something happened to Desmond. Daniel understands and asks Desmond what year it is. Desmond says 1996. Daniel tells him to go find Daniel Faraday at Oxford University. He gives him some numbers and says to remind him about Eloise.
Desmond does what he is told and at first the 1996 Daniel does not believe him, but the numbers and Eloise convince him. He shows Desmond a giant maze and then zaps Eloise (a rat) with electromagnetism (his time machine) and the rat goes unconscious. When Eloise wakes up, she immediately runs the course of the maze. Daniel explains that he just finished building the maze and that he was not going to teach Eloise for another hour. Proof that the rat's consciousness swapped back and forth in time.
Faraday explains that Desmond needs to find a constant. Something he can go back to in 1996 and 2004. If not, he will not be able to stop the jumps and eventually he will die. Desmond decides that Penny is his constant. He tries to find her and can only locate her father. Mr. Widmore is at an auction, buying a diary of Tovard Hanso, the first mate of the Black Rock, the ship from season one.
Mr. Widmore gives Desmond Penny's address and Des goes out to see her. She is angry with him for dumping her and Desmond apologizes. He says she has to do him a favor. He will leave and never come back, but he just wants her number and he will call her on Christmas Eve 2004. She thinks he is nuts, but gives him her number, which he memorizes.
When he jumps back to the present, Sayid has finished fixing the ship's phone system, but it has a small battery. Desmond calls Penny and she answers saying that she has been looking for him for three years. They say they love each other and that they will find each other. It was a very emotional moment.
Back on the island, Faraday continues reading his journal and comes to a page that says "If anything goes wrong, Desmond Hume will be my constant."
One of the things I keep thinking about: Mr. Widmore. Remember from the episode where we learn about Desmond's ability to see Charlie's death, Old Man Widdy told Des that he was not worth a glass of the expensive scotch, let alone to marry Penny. That was also the point where Desmond met the lady at the ring store, who told him that he was destined to go to the island.
Is it possible, since Widmore was buying the Hanso journal about the Black Rock, that he knows what is going on and he knew that he had to insult Desmond in order for him to get on the island, in order for him to come back and finally marry Penny? I mean, if he hated Desmond, why give him Penny's address? He just seems to be connected to everything.
On a side note, Penny is pretty hot and has a nice