For millennia, calendars have added an extra day every four years. In doing so, they violated the ancient Mayan calendar. Now we are in the 13th month of the 13th year of the new millennium, and the few who survive will battle a world of demons.

In the countryside of London, a rocket crashes on a farm and Professor Bernard Quatermass and Scotland Yard Inspector Lomax arrive in the spot. The rocket was launched by Prof. Quatermass with the astronauts Victor Carroon, Greene and Reichebheim; however only Carroon is found very sick in the cabin. He is transported to a private clinic to stay under observation despite the protests of his wife Mrs. Judith Carroon. She bribes a nurse to bring Carroon to her and she finds that he is transforming into a monster. Carroon escapes, killing people and animals during his metamorphosis while the Scotland Yard is hunting him down and Dr. Quatermass discovers that his process is an alien invasion.

Belle, her little sister, and her comatose twin brother move into a new house with their single mother Joan in order to save money to help pay for her brother's expensive healthcare. But when strange phenomena begin to occur in the house including the miraculous recovery of her brother, Belle begins to suspect her Mother isn't telling her everything and soon realizes they just moved into the infamous Amityville house.

Sophie's 18th birthday becomes a bloodbath when monsters descend upon her house and start to devour the party guests. Sophie and her friends must rally together to send their party crashers back to hell.