While returning from a mission, Thunderbird 2 is seriously damaged when it comes under attack from a new, high-speed U.S. Navy strike vessel, the U.S.N. Sentinel. After an operation to move the Empire State Building disastrously ends in the tower's complete collapse, Jeff asks that Thunderbird 4 be transported onboard the same ship to the mouth of an underground river to reach a reporter and his cameraman who are trapped beneath the wreckage.