Skull and Sidecar

It's 1926, and Nell Kelly has a couple of things to prove. First, that the skull recently found in Oregon is indeed the oldest in North America, and second that women should be taken seriously as academics. The first is confounded by a man in a literal black hat who steals the artifact at gunpoint. The second is confounded by a cultural anthropologist and notorious flapper named Gunn Flagley. In order to get the skull back and prove that herself and her science are legitimate, Nell has to climb into the sidecar of Gunn's Harley-Davidson and ride across Oregon in pursuit of the man in the black hat.
Along the way, she meets cowboys, Chinese doctors, native tribes, a religious cult, and loggers who are not afraid to cause a little chaos when the opportunity presents itself. All Nell wants is a laboratory and that skull. Is that so much for a woman to ask?