The River of Death

It's been about a year since Nico left the camps behind. He went off and did his own thing.

That is, until his father, the god Hades, made him look after his unknown little sister, Sofia.

But as Nico spends more and more time with Sofia, he learns that she has powers beyond that of any demigod and maybe even god.

Now Nico must protect his sister from anyone who might want to use those powers for their own benefit.