Nate meets his first companion when he almost lands on him. He quite literally runs into his second. He rescues his third from a desert planet with interesting ideas about slavery. His fourth...he meets his fourth when the TARDIS gets ideas of her own, and ditches him on Earth, in 2003, in Iraq, of all places.
He opens the door to a US Marine staring at him down the sight of a gun and the only thing he can think is that the TARDIS is going to require a stern talking to.
It doesn't take him long to convince the Marine, one Sergeant Brad Colbert, that he's not an Iraqi spy, because the man isn't an idiot. It does take him longer to convince Brad not to report him. He doesn't tell him about Gallifrey, or two hearts, or time travel, because the gun is still part of the equation.
When he finally talks his way out of it, gets away without a scratch on him and definitely no bullet holes, he doesn't speak to the TARDIS for three days. They go to the Barcelonas - the planet and the city - and they take a trip to the Roman empire, because he always had liked the classics, and he begins to think that that's the end of that, the end of the TARDIS having a mind of her own.
He soon realizes that's not true.
This time, when the TARDIS decides where to go herself, he lands in California, Earth, 2004. Safer, at least. Less risk of being shot, he thinks, until he opens the doors and there's Brad again, one eyebrow raised and a surfboard in his arms.
He thinks it might be a sign, a sign that this man is important, but he's looking at him like he's seen a ghost, or a hallucination, or something, and he's not sure how he can explain this. He thinks he hears the noise of the TARDIS in his head, a short burst of sound like she's saying something, even though he knows it's just his imagination and so he decides on the truth.
He gets punched, and it hurts, but he manages to get the TARDIS door open between the pounding in his jaw and the stinging in his eyes and then, finally, Brad can see her in all her glory, and he doesn't say she's bigger on the inside, and the lights seem to flicker in something like a purr of contentment when he steps over the threshold.
When Brad gets distracted by the console, by the wires and buttons and screens, hands running over them in a caress Nate's not seen before on anyone but a Time Lord, he knows he's found number four.