Colin MacLeod, the immortal Scottish Highlander, travels with the wise-cracking ghost Amergan in search of the immortal despot Marcus Octavius, who killed Colin's lover on the Celtic plains centuries earlier. The once great city of New York is now submerged under water, with only one dominant fortress towering over the sea, the fortress of Marcus Octavius. MacLeod is torn between saving the survivors of New York and hunting down his nemesis.