To save the future, she must turn to the past . . .

San Francisco, Year 3377. A deadly virus has taken the world by storm. Scientists are desperately working to develop a vaccine. And Robin Johnson - genius, high-functioning, and perhaps a little bit single-minded - is delighted. Because, to cure the disease, she's given the chance to travel back in time.

But when Robin arrives at the last Ice Age hoping to stop the virus at its source, she finds more there than she bargained for. And just as her own chilly exterior is beginning to thaw, she realises it's not only sabre-toothed tigers that are in danger of extinction . . .