When scientists on a space colony have cloned both the alien and Ripley, who died in Alien 3; in doing so, however, they've mixed alien DNA with Ripley's human chromosomes, which gives Ripley surprising power (and a bad attitude).
A band of smugglers comes aboard only to discover the new race of aliens--and when the multi-mouthed melonheads get loose, no place is safe. But, on the plus side, they have Ripley as a guide to help them get out.