Introductions.

It strikes Castle, over three years into working with the man, that he and Detective Ryan were never formally introduced. Beckett, he remembers like it was yesterday, introduced herself in the form of a gate crash and the threat of handcuffs, and Esposito had made a point of coming up and shaking the hand of the man who'd managed to put his hitherto inscrutable boss so on edge. Kevin Ryan, however, had appeared at the edge of a conversation somewhere, read out some information from his notepad, and left again, and Castle had assumed - to his shame, he now feels - that he was going to be background noise from there on in.

But over the next couple of weeks Castle noticed, bit by bit, how important this little Irish paragon was to the team. Ryan edged into his vision to take a place right beside Beckett, Esposito, the Captain, Lanie: one day it was the way that Kate, when she thought everybody was too busy to notice, looked at him, the same way she looked at Javier - like a little brother she knew had outgrown the need for her berating or mollycoddling, but enjoyed watching over anyway, just in case. Another day it was walking into the bull pen and seeing Ryan laughing with a brilliant white grin that reached his ears at Esposito and Montgomery, finishing off an anecdote that made even the Cap join in with the fist bump. Days after that, Castle's eyes are barely keeping up with the scene in front of him as Ryan chases and tackles a suspect to the ground, spouting imaginative insults and conjuring handcuffs in one fell swoop, and he can't believe it's the same man as the silly, accommodating young cop he'd seen playing Koosh ball in the Precinct.

As he looks at the Detective now, grinning at Castle brightly as he reveals the discovery of a shortcut to the Old Haunt, he is glad that there is someone at the 12th who is a slow burner, someone who lets you discover them rather than walking right up to you and making their presence known. He wonders if their friendship, if this case - hell, any case - would have panned out quite the same if Kevin Ryan had been the kind of person that squared straight up and introduced himself.