Before The Fire. The MacGregors, #2

The inhabitants of 25th century earth are dying. A deadly brain virus has taken a large death toll and it is up to one scientist to stop it. The problem for Dr. Kane Edmonds is that the form of plant-life she believes is necessary for a cure has long been extinct, dwelling nowhere else within the solar systems except the earth's past. Kane plans for every contingency when she agrees to travel through time to hunt down the life-saving plant.
Every contingency, that is, except for her attraction to George Wyndom, the dark and formidable Earl of Blackmore.(originally published under the pseudonym Tia Isabella)