I like Arjan's theory - it means that Nemesis has multiple plans going, and makes it seem like a credible opponent for Mab. Uriel (presumably) makes sure that Harry and Michael are there to take the hobs out - but there's one problem: Harry's been cut off from his blasting rod at this point - and I'm not sure whether Harry's pulled the Catnip Trick yet. If he hasn't then that's how the Gruffs tracking him, but if he hasn't, then how are they there?