Tentacles, by Roland Smith (2009, Scholastic, upper middle grade on up, 319pp)
In Cryptid Hunters (2006), Smith introduced Marty and Grace, the young wards of their uncle, an obsessed cryptologist, who travels the world looking for evidence that "mythological" creatures are actually real. In this case, the creature in question is a dinosaur, and, after confronting an evil villain who seeks to kill, rather than conserve, the marvellous creature, the twins and their uncle successfully save two dinosaur eggs.
Now Marty and Grace, and Marty's best friend Luther, have signed on for another cryptozoologial quest. This time around they are on board a possibly haunted research vessel in the South Pacific, hunting for the Kraken, with the dinosaur eggs in tow. It is anything but a peaceful scientific expedition, as it becomes clear that a saboteur is on board, the dino eggs are hatching, and the same bad guy they met in the Congo is pursuing them once again...
Despite the science fictionesque elements of dinosaurs and giant squids, this book is much more the action/adventure type genre, the sort of book in which clever kids, with some neat science on their side, try to foil the bad guys. The story moves briskly with touches of humor, the suspense mounts nicely, and, all in all, it's a well-told story with plenty of twists that should have great appeal, in particular, to upper middle-grade boys
I say this, incidentally, not simply because boys might be more drawn to action/adventure books with lots of cool technology. Marty and Luther, the guy pals, felt much more front and center than Grace, and their boyish interactions, which included too much reiteration of their pet phrase "duh du jour" might be a smidge annoying to the girl type reader (or, for that matter, to the reader in general--like Jack at Book Review).
There is no need to have read Cryptid Hunters--Smith does an excellent job of gracefully working in what the reader needs to know.
Other reviews and comments at Readingjunky's Reading Roost, Lauren's Book Stop, and, most interestingly, a rave review here at the blog of the International Crypto Community, Still on the Track.
(Tentacles was nominated for the Cybils Award in middle grade sci fi/fantasy, and I received my copy from the publisher in my role as a first round panelist in that category)