An "ingenious, horrifying" (The Guardian) first contact story by one of the twentieth century's most brilliant--and neglected--science fiction and horror writers, whom Stephen King called "the best writer of science fiction that England has ever produced." What if aliens colonized Earth's oceans, rather than its land?

Britain, 1953: It begins with red dots appearing across the sky and crashing into the oceans' deeps. Ships begin sinking mysteriously. Then an envoy sent by submarine to establish peaceful communications is killed. Mike and Phyllis Watson are a husband-and-wife journalist team who initially believe that the aliens' interest in the ocean's floor, a high-pressure environment that is uninhabitable by humankind, means that the two species may peacefully co-exist. But as "sea tanks" emerge from the sea and begin raiding coastal towns--and as the polar ice caps are intentionally melted, raising sea levels everywhere--it becomes clear that these aliens are not interested in sharing, and that humankind might just be on the brink of extinction.