'Spy'? That's certainly an idea...and it would of course be supremely insulting! But I don't think the circumstances really fit--nothing in BPC's thoughts, which Broster does show us, indicates that he thinks Ewen isn't loyal, just that he's loyal in his own irritating, overprotective way. I would have expected something more along the lines of 'nursemaid', but that's too long and doesn't begin with 's'.

Not replying in rot13 since it's not a spoiler for future chapters, but: I do wonder why Keith uses the title 'Prince' at the end! Properly he should say 'Pretender'. A little slip of the tongue from spending too much time among Jacobites, Keith? *g*