Allen is a postal inspector sent to California to find out why mail delivery is taking so long. It turns out that black hats Withers and Barcroft are behind the wrongdoings. The plot turns to a race between Allen on Koko the Miracle Horse on land and Withers and Barcroft traveling via ship.
The object is to see which method delivers the mail most efficiently. Allen also saves an innocent man from being hanged with not a moment to spare. With all this in less than an hour, you can get tired just thinking about it.