I'm reading "Grave Peril", currently at the party at Bianca's, where Lea claimed Harry broke the deal he made with her three times: one years ago, one a few days back, and one just a day ago or so when saving Charity Carpenter at the graveyard.
I remember two of those (years ago, when fighting Justin or his demon, and the one when saving Charity), but when did the third (technically second?) one happen? The only meeting they had in the meantime, that I remember, was when going after Agatha Hagglethorn's ghost in the Nevernever (from the hospital's maternity ward), but I don't remember Harry promising anything to her back then? (unless "I will go with you... when Hell freezes over!" somehow counts?)