The Southern European thread, or Western South Europe and South Central European thread, or perhaps more appropriately, the South-central and southwestern European thread involves characters introduced in the short story To Dye For by Mercedes Lackey but the thread plot action proper kicked off in the second published novel sequel of the series, the best selling 1634: The Galileo Affair and its direct sequel, 1635: The Cannon Law, both co-written by Flint and Andrew Dennis. The thread continues in 1635: The Papal Stakes, co-written by Flint and Charles Gannon.

The main characters are in part, Lackey's Stone family, combined with Flint's Sharon Nichols and Lawrence Mazzare.