When last we saw Atticus O'Sullivan, he was getting an old friend off an island in Tir Na Nog where time runs slower than it does for the rest of the world. Thus why Owen Kennedy, who should have died a few millennia ago, is still alive and berating Atticus. (Owen, who's real name involves symbols I can't find on my character map, is Atticus's Archdruid from back when Atticus became a druid.)
Owen has much catching up to do, particularly since he doesn't speak English or any modern language. which leads to much fish out of water comedy in the first part of then book. This improves after Owen hooks up with a werewolf and goes to Tir NaNog to present himself to Brighid, where he also delivers a message for Brighid that came from the Morrigan as he was put onto his time island.
Granuaile, in the meantime, is dealing with the witch who had possessed her earlier in the series. Laksha calls Granuaile with news of Gran's father. Seems Daddy has been taken over by a raksoyuj, and said possessor is summoning as many rakshasas as he can, creating a very strange plague in the area of India that Gran's father had been digging in. (i.e. people getting possessed by rakshasas and appearing to be very sick.) This plot line eventually leads Gran to the Himalayas to get a weapon of water magic, from one of the other supernatural races making minor appearances in this book.
Atticus's plot takes him through both Gran and Owen's plot, but detours into Japan for a meeting with Inara and her kitsune helpers. It's here that Atticus finds out about the 9 gods who are intervening with him to stop Ragnarok.
By the end of the book, not only have we met Durga on the Indian subcontinent, Hearne has redeemed his portrayal of Loki (in previous books, the freaking trickster archetype has been going full steam ahead with direct confrontation and blowing stuff up like a Die Hard movie. Which was annoying, particularly after his fabulous portrayals of Coyote earlier on in the series. In this book, we get some exposition that redeems to portrayal.), and we have a much better idea of what set the current story arc in motion and why. We also learn that have Bane sidhe written into a battle tends to create spoilers, since they wail out the doom of the fallen.
Something I'm noticing here that's becoming the formula for series urban fantasy is that it's like reading a long running D&D campaign after a while. We start with small confrontations that lead to boss fights. Then, as things progress and the characters become more knowledgeable, we begin to see a larger plot spread across the campaign, and may journeys to reach a finishing point. Perhaps this is a modern take on Campbell and his Hero of 1,000 Faces. But once you see the monomyth appearing, it becomes a case of how entertaining the telling of tail is. In this case, Hearne is telling his version of the myth in a compelling and fun way. I look forward to seeing what the next volume brings.