Peter is the sibling that Nicola likes best, after Giles, and as she's the one he likes best (after Giles) too, it all works out nicely. Or at least, it works out nicely in AF's prose as opposed to my half remembered mangling of it.

I think we get that comment in Marlows and the Traitor, before they go out and get rained on together. Possibly in the same para as the Lawrie comment.