Etri to Mab: order your vassal to release Thomas from the island, he is your responsibility.
If you want to have a criminal who is locked up in a foreign country you ask the government of that country not the governor of the local prison.
Yeah, but why should Mab listen to Etri? Under Faerie rules, rescuing Thomas was a favor given to Lara. I don't think Mab is going to go back on that.
Also it could be argued that Warden of Demonreach is a position Harry holds entirely separately from his position as Winter Knight...
I mean, the Svartalves are nothing to mess with lightly, but I can't see them having any leverage over
Mab.
If Harry had been
spotted rescuing Thomas during the talks, it would have been an embarrassment/loss of face to Mab. But now, especially given that the actual talks are now irrelevant?