Island in the Sea of Time is a science fiction novel by Canadian-American writer S. M. Stirling, the first of the three alternate history books in the Nantucket series.

At 9:15 pm EST on March 17, 1998, a circular region, including the island of Nantucket and the United States Coast Guard cutter Eagle sailing nearby, are transported by an unknown phenomenon (called "The Event") back in time to the Bronze Age circa 1250s B.C.

Meanwhile, Captain Marian Alston takes the Eagle to Great Britain, with ancient Greek speaking classics historian Ian Arnstein and Lithuanian-speaking Doreen Rosenthal as interpreters, where they trade Nantucket-made goods with the Iraiina for grain.

While the people of Nantucket work for their survival, the ambitious and ruthless Lieutenant William Walker of the Eagle decides that with modern technology he could become a king.

With the help of Isketerol and others, Walker convinces some naive environmentalists to steal a ship and kidnap Cofflin's wife, so they can give the benefits of modern culture to Native Americans.