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 (Charles S. Dutton) 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 (Carla Gugino) is the contingency analyst responsible for monitoring, and acting on, the potential global crisis. Her handpicked specialists include Dr. Nigel Fenway (Brent Spiner), a NASA microbiologist; Lucas Pegg (Rob Benedict), a brilliant physicist; Arthur Ramsey (Peter Dinklage), an expert in languages and mathematics; and Cavennaugh (Brian Van Holt), 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!