Seth Gecko, one of the two survivors of the movie From Dusk till Dawn, has been condemned to death for the murders his dead brother Richie committed. He is now an inmate of the fictional Rising Sun high-security prison, a converted tanker floating off the coast of New Orleans.
Vampires infiltrate the prison by posing as inmates. They murder the transport guards and the warden and begin a rampage. In the chaos, Seth gains a weapon and escapes his cell.
At the end, Seth kills the vampires and escapes the prison along with the other survivors.