Summer's Crossing (The Iron Fey #3.5)

A Midsummer's Nightmare? Robin Goodfellow. Puck. Summer Court prankster, King Oberon's right hand, bane of many a faery queen's existence—and secret friend to Prince Ash of the Winter Court. Until one girl's death came between them, and another girl stole both their hearts.

Now Ash has granted one favor too many and someone's come to collect, forcing the prince to a place he cannot go without Puck's help—into the heart of the Summer Court. And Puck faces the ultimate choice—betray Ash and possibly win the girl they both love, or help his former friend turned bitter enemy pull off a deception that no true faery prankster could possibly resist.