Last summer I read a book (I think it was written sometime between 2014 & 2016) about this boy whose friend (a girl) was taken by slavers. He travels with his mother -- his father is a drunk and a thief -- through the wilderness to a new city where he trains at a military academy so that he can go back and rescue his friend.
Along the way, he and his companions find giant animals and begin to learn arcane skills. While he travels, trying to learn military and magical skills, he is also trying to solve the mystery of the rise of these magical, giant animals. They even travel to an abandoned, forbidden city where some of his companions are eaten by a monstrous snake, which mysteriously doesn't eat the protagonist.
What's the name of this book? I can't find it!