Atlantis Unleashed (Warriors of Poseidon, Book 3) by Alyssa Day
Eleven thousand years ago Poseidon’s warriors took an oath swearing to protect humanity from those who stalk the night. Now powerful forces are uniting and it all comes down to a warrior prince and a woman of science; these two souls are all that stand between justice and the eternal darkness.
The Sea of Monsters by Rick Riordan (Kindle Edition)
This is the Kindle version of the second book in the “Percy Jackson and the Olympians” series. Summer is the time for all young heroes to gather at Camp Half-Blood to train in the art of survival against the monsters that live in the real world seeking to destroy the young demigods. It is called Camp Half-Blood because it is a safe place, a summer camp, specifically for young campers with one mortal parent and one parent who is a Greek god.