Alice Payne Rides by Kate Heartfield

After abducting Arthur of Brittany from his own time in 1203, thereby creating the mystery that partly prompted the visit in the first place, Alice and her team discover that they have inadvertently brought the smallpox virus back to 1780 with them. Searching for a future vaccine, Prudence finds that the various factions in the future time war intend to use the crisis to their own advantage. Can the team prevent an international pandemic across time, and put history back on its tracks? At least until the next battle in the time war…