Arthur wants to create an embassy on the American coast. That way Atlantis and the surface world will be able to learn about each other diplomatically. He asks Mera to head the mission. She reluctantly agrees.
Meanwhile a mysterious creature has been killing people on land. The attacks look like shark bites, which is odd because many of the killings have been happening on land, away from the sea. The FBI calls on Arthur to solve the case, which brings him into contact with Dead Water, a creature that can teleport through the tiniest drop of water. When Arthur discovers Dead Water used to be a man, he must go to extremes to stop him (including keeping the man extremely dehydrated so he won't revert back to Dead Water) and find out what happened.
I've been reading Rebirth since it started, but I missed all of these stories. It's nice to finally be caught up (and to know where Dead Water came from). I'm still waiting on that war of the seven seas promised at the end of Volume 4 though).