I am on a sequel roll these days. Ironside is preceded by Holly Black's Tithe which I did like. I admit I get These Modern Faery's Tales confused sometimes with Melissa Marr's Wicked Lovely books because they both have that same dark, two faery court thing happening. I like them both, but Black's novels are darker and a bit creepier.
At the end of Tithe, Robein is set up to be the new king of the Unseelie Court but his former lover and queen of the Seelie Court is not really happy with that whole scenario. Kaye, Robein's new girlfriend (who importantly knows Robein's true name which gives her complete control over him) is also a pixie and wants to be Robein's consort. To become so, she declares herself to him and he gives her an impossible task to complete to show her worthiness to be his consort...this is all according to the faery traditions. So Kaye is sent out to find a faery who can lie. And no faery can lie.