The Tomb of Shadows

Lerangis, Peter. The Tomb of Shadows (Seven Wonders #3)
May 13th 2014 by HarperCollins 
Book from Young Adult Books Central and reviewed there.

Jack, Cass and Aly have reason to believe that Jack's mother did not die falling into a crevasse on an expedition, and think that she is working with the Massa. When they infiltrate one of their bases, it is deserted and then blows up. The kids aren't too badly injured, but Torquin decides they should head to Karai Institute headquarters to regroup. They run into Dr. Bradley and Professor Bhegard, whom they still don't trust-- he has tried to cure their condition, but they aren't sure of his motives. He is gravely ill, and the group try to locate the third loculus, which is supposed to be a healing stone, in order to help him. To do this, they are taken on a trip to the underworld by the zombie-esque Skilaki, who claims that Queen Artemisia has the stone. Even though the whole trip is perilous, it is also unsuccessful, and they escape and try to figure out where the stone is. They decide that it is in a museum, and with the help of the troll like Canavar they head to New York to get the stone and try to locate Jack's mother, but the Massa are still standing in their way.
Strengths: This is a good action/adventure fantasy with a healthy does of mythology. The characters are fairly individual, and the plot moved along well. I don't mean to damn this with faint praise; I just suffered from such bad fantasy amnesia that I didn't even review the first two books, so it was hard to get up to speed. There will be seven books in this series, I think, and they are good to have on hand for avid fantasy fans who have read other long series.
Weaknesses: Cass's talent of speaking backwards is just annoying.