A group of explorers are sent to the Antarctic when it's believed a vast reservoir of oil has been uncovered. However, all contact is lost with them. Another group of them is sent in, including petrobiologist Aimie Weir, whose boyfriend was in the first group. There are also soldiers, led by Alex Hunter. He was almost killed a few years before by a Russian agent--and the bullet lodged in his head has messed up his pituitary gland, so he has near-superhuman abilities. Let's just say that his skills end up being necessary for any survivors.
What they discover is a vast cave system beneath the ice, a hidden lake inhabited by uniquely evolved creatures. At the top of the food chain is a monster that has evolved from squids. It is highly intelligent, can travel in water and over land, and its tentacles can mimic the form of its prey. This is all basically a reworking of Jules Verne's Journey to the Center of the Earth. Fans of James Rollins and Steve Alten will enjoy this.