V.E Schwab 
Shades of Magic 
The Steel Prince #8

Despite being battered and wounded, Prince Maxim Maresh has successfully bested the first three trials of the Night of Knives, using his wits and magical skills. However on the threshold of the fourth and final room, Maresh remembered the advice of his comrade, Isra, and turned his back on the tournament. But before he could leave he was pulled into the doorway of the fourth trial by a powerful magical binding spell…