Sam and the Doctor were now closer friends than anyone in the history of the universe. They now spent all day with each other and lost track of time, the Doctor often staying at Sam's apartment past 2:00 a.m. The Doctor had discovered his favorite movie series, which was Star Wars. He said that the Death Star reminded him of the eye of a Dalek and that the stormtroopers reminded him of Cybermen. Sam had never seen any of the aliens that the Doctor often told him stories of, but he did his best to imagine how they looked.
One day, the Doctor decided to let Sam in on how he was feeling, pertaining to his sense of incompleteness. They were at Sam's apartment sitting on the couch, watching the movie "Life of Pi". Once it was over, he began. He told Sam that he made a promise when he assumed the name and role of the Doctor, and he wasn't about to abandon that promise for the sake of amusement parks and Star Wars. Sam, of course, completely understood. He looked the Doctor in the eyes and gave him an offer.
"Take me with you." he said, "Take me with you, and we can roam the stars and defend those in need. We can be the greatest duo in spacetime history, but only if you'll let it be. Take me to the Tardis; show me the stars, Doctor." And with that, slowly and imperfectly, Sam leaned in and gave the Doctor a kiss. It wasn't very long, and it wasn't all that magical, but it was what they had both silently wanted since they met each other those five weeks ago. It was a split second of simple completeness in an incomplete world. It made the Doctor's mind up instantly, without him giving it the slightest bit of thought. He looked Sam in the eyes and smiled the most famous of smiles. He reached around his neck and held in his hand a key. He said to Sam, "Do you know what this is, Sam?" Sam simply shook his head, and the Doctor said "This, my companion, is a key. Now it isn't a special key, and it isn't magical. But this key will unlock the future that we can unfold. Are you ready?" Sam smiled and said "Let's do it." And with that, they sprang up off of the couch and out the door, Sam not stopping to make sure it was locked and he has the key. The Doctor ran, and Sam followed. They ran and ran for at least a mile, and Sam stopped when he noticed the Doctor standing in front of an old police telephone box. In all the stories the Doctor had told Sam, he never did tell him what the Tardis looked like. He didn't have to. Because once the Doctor held the key and looked at the box with aspiration in his eyes, Sam knew. This was the box that had seen and survived the Time War. This box had been nearly everywhere there was to be; the places it hadn't been were the places they'd go. This was the box that would seal their fate - forever time warriors in an endless battle to save the universe, one problem at a time.