Tess Conway was a wealthy heiress to an estate located on Matinicus Island in the state of Maine. She financed an expedition to locate the Water-Clock of Thoth, an ancient Egyptian artifact that was eventually discovered by the Egyptologist Dr. Hargrove. However, during the night of summer solstice in 1932, Tess attempted to use the artifact and mysteriously vanished as a result. Many years later, a former student of Dr. Hargrove arrives on the island, only to discover that it has been overrun by horrifying creatures. He must explore the estate and its surroundings, and find out what really happened on the fateful night.

Killing Time is a 3D first-person shooter differing in several ways from the traditional template of Doom. Rather than being divided into successive levels, the game's world is fairly open, allowing the player to explore locations in different order as well as backtrack to previously visited areas. The game's arsenal includes, besides various guns and Molotov cocktails, unique weapons such as an Ankh that damages multiple enemies at once. Various setpieces may involve sudden attacks by large amounts of enemies, traps, etc. The player character is able to jump, strafe, and crouch, and those actions are required in certain places. The spirits of Tess and her guests appear occasionally and bring the story of that night to light, helping the player to find keys, unlock doorways, locate secret passages, and solve puzzles.