It's Amy who finds it. Rifling through a back cupboard of the Tardis' infirmary for an aspirin (it's as if the Doctor deliberately forgets that his companions are human), she comes across a box full of morning-after pills, topped with a neat chart that has the time and date every time that one has been signed out. A glass of water and a quick swallow later, she's wandering into the console room with a clipboard in hand, much to the confusion of Rory and the Doctor.
Missing Rory calling her name, Amy notices with amusement that a majority of the pills have been taken out by a Captain Jack H., with the last three dated to 1336 (Amy wonders how long this Captain was in Japan.)
"Amy! Amy!" This time, it's the Doctor waving his hands in front of her face and trying to snatch the clipboard from her arms. She pulls it back, smirking at the Doctor.
"Sooo, Doctor, I take it it's pretty common to have people shagging on the Tardis?" She runs her finger down the list, noting several instances where a Rose Tyler has taken a pill at the same time as the Captain.
"Amy, no!" His hands are flying all about the place, nearly smacking Rory's raised eyebrows off his face. "Well, I don't ask what you and Rory do, with your kissing and such, but no! You're my Amelia Pond! That just shouldn't happen!" His ears are tinting pinker and pinker as his voice rises.
Rory groans now, "Doctor, where exactly did you think your wife came from?"
"And besides," adds Amy, "none of the Ponds are named Jack or Rose."
The Doctor freezes at this, then stalks over to his favourite Pond, seizing the chart for real this time. The colour drains from his face and the knuckles gripping the clipboard almost painfully.
"Doctor? Anything Rory and I should know? Did these people used to travel with you? And why would a Jack need morning after pills?"
"1941. 1941. That's when the first entry is." Suddenly he's a flurry of movement, legs propelling him to the console, hands and chin and toes throwing switches and pushing buttons at the greatest speed. Amy shoots Rory a worried look as the Tardis is catapulted into flight, its careening more extreme than usual. But the trip is shorter than expected, and Amy suspects that they have not travelled out of 2018, only to somewhere else on Earth. Antarctica perhaps? Or maybe the aforementioned Japan. Or possibly, finally, Rio. The Doctor is out of the double doors like a rocket, the still-dizzy Ponds stumbling after him to see-
"Cardiff?" Rory asks bewildered. "Why Cardiff?"
"JACK! JACKKK!" The Doctor is bellowing, but there seems to be no point as an extraordinarily handsome man runs up to him and crushes him in a massive hug, whooping all the while. The man, apparently the Captain Jack H. of the log, pulls back with a grin, and suddenly the Doctor's fists are in his face and he's flat on his back, being pummelled by a red-faced Time Lord.
"You know, I've always imagined you straddling me, but it was never quite like this." Jack appears unconcerned by his bleeding lip and effortlessly sits up, the Doctor's element of surprise now gone. Jack easily catches the Doctor's hands and holds them away. "Another new face? I'm not saying I didn't miss you, but I'd appreciate if you weren't trying to break my money-maker."
With a clenched jaw, the Doctor rocks back to his haunches and then stands, followed by Jack, who's gingerly let him go.
"Rose." One word, with the Doctor poking Jack in the middle of his chest, but it's enough to make Jack perk up.
"Rose? Is she back? Did you see her?" Amy shoots a questioning look at Rory. The Rose from the chart? Rory shrugs, as perplexed as his wife.
"No, Rose. And you. In MY Tardis." The Doctor's hands are clenched at his side; Jack picks up the signal and takes a hasty step back.
"Ah. So you know."
"Yes! Yes I know! Why didn't I know before?"
"Um, hate to interrupt, but what exactly are you talking about?" Rory cuts in.
"Well, a couple faces ago, the Doctor and I were travelling with our best friend, Rose, and, you see," Jack kind of looks sheepish, "the Doctor was in love with Rose and never told her-"
"I never said that!"
"-exactly my point. And she never told him she loved him back. And I was in love with the both of them, and well, a few glasses of champagne later, Rose and I shagged atop an invisible Chula ship and didn't really stop until I died the first time."
"You knew." The Doctor presses his lips together. "You knew how I felt and you two still did that. On MY Tardis."
"Ehhh, we knew you would never make a move on either of us and, you know, it's not like we could really bring anyone else onto the ship to relieve our frustr-"
The Doctor's fist is once again making a connection with Jack's jaw.