The first night she stays at his apartment is awkward.

The night itself isn't awkward; Beckett thanks him for letting her stay there, and goes to sleep in what used to be Martha's room. The awkward part comes when Martha herself bursts through the front door to the embarrassingly domestic scene that involves Beckett cooking eggs and bacon before Castle had even gotten up. Both Castle and Beckett insist that nothing happened between them. Martha isn't convinced.

The second night is less awkward, and the third and fourth are even better. Every so often, though, there is a tense moment over dinner as Castle and Alexis share an inside joke that Beckett doesn't get, or another when Beckett accidentally puts the Windex in the wrong cabinet.

But eventually, after a few weeks, things settle into a routine. Castle notices this when he comes home one evening to find Beckett quietly working on case paperwork and Alexis finishing her math homework at the kitchen table, each silently enjoying the other's company. And after that, Castle starts to notice more of these little things, like when the three of them laugh together while watching game shows over cartons of Thai food one Thursday evening, or when it is Beckett, not Castle, who gives Alexis a ride to fencing practice.

Then one day, Beckett gets the call. The renovations are complete, and she can move back into her apartment at any time.

There is one more day of laughter and enjoying the built-up closeness as Castle and Alexis help Beckett pick out new furniture for her place, but the day is over all too soon and before anyone knows it, her things are packed into boxes and then suddenly gone.

It might have been awkward when Beckett first started living with the Castles, but now there's a hole in the family that Castle knows only she can fill.

But he isn't worried. As Beckett hugs him and thanks him for letting her stay at his place for so long, he smiles. The next time she comes to stay at his place, he knows it will be permanent.