An astronaut gets infected with alien DNA during the first mission on Mars and runs amok on earth. Preston and Laura team up with a peaceful, genetically re-engineered Sil to track the monster down.

In 2019, a mercenary pursues a man and woman who escaped a research facility after learning their true fate.

Two centuries after her death, a powerful human/alien hybrid clone of Ellen Ripley aids a crew of space pirates in stopping the aliens from reaching Earth.