The U.S. Navy makes a chilling discovery: an extraterrestrial craft has landed in the Atlantic Ocean. As a result, Deputy National Security Advisor J.T. Baylock must quickly assemble a team of experts to prepare for the possibility of an unprecedented crisis situation--an alien invasion. The response plan activated by the government is dubbed "Threshold"--And the gathered members of the team are experts in their individual pursuits. Dr. Molly Anne Caffrey is the contingency analyst responsible for monitoring, and acting on, the potential global crisis. Her handpicked specialists include Dr. Nigel Fenway, a NASA microbiologist; Lucas Pegg, a brilliant physicist; Arthur Ramsey, an expert in languages and mathematics; and Cavennaugh, a skillfully trained covert operative. Together they must unlock the mysteries--and determine the intentions of--the strange, other-worldly visitors now here in our midst.