Whatever bet Alec and Magnus took part in is totally up to you. But clearly, whatever it was, Alec lost and has to wear the floaties of shame. THAT INFERNAL DEVICE LOL
This person didn't notice this till they were rereading Clockwork Prince and saw the chapter name and thought about City of Ashes so in Clockwork Prince chapter 13 is titled the Mortal Sword. City of Ashes chapter 7 is titled the Mortal Sword.