Rayph Ivoryfist is the Gandalf-esque protector of his kingdom and has done for untold millennium. Unfortunately, his pride has gotten in the way and gotten himself exiled from the courts due to the current ruler being a petty spoiled tyrant. This means he's not paying attention when a magical prison filled with the worst criminals in the world, basically magical supervillains nearly impossible to kill, gets raided and freed. Rayph must assemble a team to go after them and deal with the fact no one wants his help but they desperately need it.
Song really reads like a fantasy comic book with its share of legendary heroes and badasses getting back together for one last ride. It's the equivalent of assembling a new Justice League after a mass breakout at Arkham Asylum. All of the heroes have their own struggles to deal with ranging from loyalty to their awful king to the fact their child is dying from a horrible disease growing from her infected legs.
The biggest appeal of the book is the melodrama of Rayph who is a little too set in his ways and idealistic to really deal with mortals along with their ignorance. He is pompous with the locals who want to form a lynch mob against the genuinely terrifying witch nearby and confronts the king to humiliate him despite the fact it would probably be better to work around him. It's a nice way of doing a heroic figure whose very better qualities make him a flawed individual.
The book could have benefited from a bit more exposition as while the world building is there, it's in the conversations. I think it would have just been easier to give some paragraphs describing what the kingdoms and their beliefs are. I found out they worship Tyr as their God of Justice (like in Forgotten Realms) only about halfway through. On the other hand, I think some fans will enjoy the "show, don't tell" nature of this.
I also like the way magic is portrayed in this universe as it's genuinely intimidating. If you manage to master it, you're basically immortal and only have to worry about your fellow mages to deal with for the rest of your life. I also like the implications of this with prisons as ways to contain evil doers for all time as opposed to simply killing the bad guys. In most fantasy, you don't have dungeons that contain villains since death is usually the punishment for bad guys.
In conclusion, this is a fun and well-written novel that sets up the events for what I suspect is a longer series. It's a bit underwritten for my taste and sometimes confusing but the action is good, the characters are interesting, the heroes likable, and the villains hateable.