The time-displaced island of Nantucket is facing a threat from Tartessos, a kingdom in Spain that has been rapidly "modernizing" under the rule of a friend of series villain, William Walker. Contact is made with the kingdoms of Mycenae and Babylon, and an expedition prepares to follow in the footsteps of Lewis and Clark.
This story is followed by the end of the trilogy, On the Oceans of Eternity.
Against the Tide of Years provides examples of:
- Citizenship Marriage: The Republic of Nantucket reluctantly agrees to allow Kat Hollard to marry King Kashtiliash in order to cement an alliance with Babylon.
- Oh, Crap!: When Kenneth Hollard discovers that he's been chosen to be the consort for Raupasha, the de-facto Queen of the Mitanni.
