Book 4. Spoilers continue.
It opens at a leisurely pace, with Winston, the fireshaper/priest from the last book coming by looking to buy a place, and questions about why someone left. But Hades has not shown up again, which can only mean bad things.
It involves asking Thanatos questions, Cerebus's passionate desire to help, the secret behind Lexi's tattoo, a stranger who helps out of nowhere*, Hestia's secret, a very truncated text message to Lexi, Apollo's searching for something to help Zeus, memories of the dead, the question of rescuing Jake, and more.
*sage souls will recognize from info in the first book.