“The Bookseller” can be found in The Best of Roald Dahl (Vintage).
“Only connect” is a reference to E.M. Forster’s novel, Howards End: “Only connect the prose and the passion, and both will be exalted…”
“We read to know we’re not alone.”
This phrase (or variations of it) is often attributed to C.S. Lewis, but really Anthony Hopkins (as C.S. Lewis) says it in the movie, Shadowlands, written by William Nicholson.
A Wrinkle in Time by Madeleine L’engle
Cloud Atlas by David Mitchell
“like a retired cop character in an Elmore Leonard novel” — Lambiase might be thinking of Out of Sight.
“that famous C.S. Lewis quote tattooed on [Jacob Gardner’s} wrist”
There are several possible answers to this question, and I almost hate to narrow it down to one. Perhaps it’s silly, but I like readers to be able to imagine whatever quote they’d like on Jacob Gardner’s wrist. A reader could imagine, for instance, that Gardner tattooed the Nicholson quote on his wrist, not knowing that it was from the movie until it was too late. However, I think Gardner is a more precise person than that and, if pressed, I think it most likely comes from the dedication of The Lion, the Witch, and the Wardrobe: “Some day you will be old enough to start reading fairy tales again.”
I do not know of a literary crime novel about “an Amish girl who disappears while on Rumspringa,” but it could certainly exist.