That's a storytelling perspective that would make me want to throw up on a best day, but in a show about time travel, the hardest thing to write in all of science fiction -- besides, apparently, a woman made of anything other than cardboard or external harddrive -- it's just sort of chillingly careless.
Anyway, the Doctor's gotten clever about getting the TARDIS to Space 1969, somehow, and at some point he has intuited that they're all lying to him, so he gets very scary and intimidating for a while. "Don't play games with me. Don't ever, ever think you're capable of that," he says, and "Dr. Song, just one thing: Who are you? You're someone from my future, getting that, but who? Why are you in prison? Who did you kill? I love a bad girl, me, but trust you? Seriously?" All of which has nothing to do with River and everything to do with this:
Amy: "Trust me. You have to do this, and you can't ask why."
Doctor: "Are you being threatened? Is someone making you say that? Swear to me. Swear to me on something that matters."
Amy: "Fish fingers and custard."
Aww. Why go for the thing with teeth when you can push the same sentimental button you've already pushed eleven times? (Luckily, this show is basically only about the chemistry between these two darling actors anymore, so it works.)
Anyway, this Canton Everett Delaware III is very important. How do we know that? Because the characters keep saying it over and over. Why do they keep saying it over and over? So we'll know he's important: Canton Everett Delaware III, Badger Lampkin, has been kicked out of the FBI for reasons we'll maybe never learn -- "I understand you have a problem with authority," the Doctor says approvingly -- and, as we see in intercut scenes during their expository discussion aboard the TARDIS, Nixon has summoned him back to do extra-secret work.
If you're not familiar with Richard Nixon, don't worry about it. Neither does the show. This story has all the historical acumen and insight we've come to expect in the last year or so:
Doctor: "Vietnam, Watergate..."
River: "There's some good stuff, too..."
Doctor: "Not enough."
So the secret thing that Canton needs to investigate is how the President keeps getting mysterious phone calls from a mysterious child, even though there's no way for him to get direct calls in the Oval Office. So what you have is not only a mysterious spacesuit like in "Silence In The Library," but also mysterious spooky imperiled voices, like in... Oh, every Moffat episode, really. (But if you're thinking the "Silence" in the Library has anything to do with the "Silence" of this and last season, think again. That would imply a plan of some kind, and not just a dartboard full of cool shit.)