Lynn Trevor, president of Cedarcliff's bank, has disappeared, and his father hires Tam O'Brien (professionally known as Tam o' Shanter) to investigate. She goes undercover as a nurse, and soon finds there is more than enough reason for grave concern. Multiple professional and personal motives arise for getting rid of Trevor, and when a body is finally discovered, Tam must use all her skill and resources to uncover the truth.

Tam O'Brien, as a young female detective, breaks more than a few of the literary cliches of Golden-Age Detective Fiction. She is smart, capable, well-trained, and unsusceptible to the allure of passing romance if it's going to get in the way of her job. Her father, Rance O'Brien, is an ex-Chief of Detectives on the police force, so she grew up surrounded by officers and detectives. Inspector Pete McCoy is an old friend, willing to discuss and debate a case, though not above a little friendly competition. Dips is the young, streetwise lieutenant of her inquiry agency.

The Hollow Tree Mystery was published as a magazine novel in 1930.