Release Message:  The Doctor, Tegan (Janet Fielding) and Turlough land inside an undersea secret military base in wartime Earth, 2084.

Description:  The Doctor, Tegan and Turlough land inside an undersea secret military base in wartime Earth, 2084. The base is about to be attacked on two fronts. Enemy agents within work to neutralize the base while an assault team of aquatic Silurians prepare without for a surprise attack.