Waking up at the Bottom of a Lake

When Arthur woke up at the bottom of a lake only to be saved by a giant tentacle monster, he was upset. When he dragged himself up to his castle and found that it was a school for sorcerers- he was upset. Now he has to play nice with them and wait for his best friend and the most famously powerful warlock in existence - Merlin Famous! - to find him and figure out why he has woken.