Saving Old Hickory. Tempus Viatores: The Acolytes of Clio, #4

Four books of slow burn. One question left. He finally asked. Alex Lindgren said yes. After everything - Herculaneum, Washington DC, medieval Morocco, and every timeline in between - Titus finally asked, and Alex said yes. They deserve five minutes to celebrate. They don't get five minutes. A radio broadcasting from a version of 1917 that shouldn't exist pulls them back to Greenville, South Carolina - and straight into the ranks of the 30th Infantry Division, the soldiers who will earn the nickname Old Hickory.
Their mission: stop Manwell, an immortal son of the German deity Mannus, from rewriting the war before the soldiers even reach Europe. Manwell's plan is elegant and horrifying: unleash the Spanish Influenza on Old Hickory months ahead of schedule, crippling the division before they ever ship out, and tip the balance of the war toward a German empire. This one isn't Fortuna Atrox - Manwell is newer, hungrier, and has something to prove to every immortal watching.
While Titus trains alongside soldiers who have no idea what's coming, Alex embeds with the volunteer nurses preparing to cross the Atlantic - gathering intelligence, building trust, and fighting a biological threat with no good weapons against it. Together, they must untangle Manwell's timeline sabotage before an early epidemic makes the history they've been protecting unrecognizable. The war is dangerous enough on its own.
Adding an immortal with a god complex and a weaponized pandemic makes it considerably worse. Perfect for fans of Doctor Who, Outlander, The Librarians, and Warehouse 13.