Ninety minutes, twice a day. Five days a week. And they hate each other.

Car pool heaven turns into car pool hell when Anthea Rossignole realizes her lover is having an affair with the other woman sharing their daily commute. Anthea's corporate career as a cost analyst is the only thing keeping her together. Now she's looking for someone to share the long drive in the Bay Area's notorious traffic.

Shay Sumoto desperately needs a car pool. Though wildly overqualified, the environmental biologist takes a job testing well samples to keep body and soul together. The debt from her father's terminal illness and the loss of their company have left her with no money and no sense of humor.

When Shay and Anthea begin carpooling together, their instant antipathy gets even worse. But when Shay uncovers alarming test results in her work—information that could cost both of them their jobs—Anthea is the only person she trusts for advice.