Reading-of-the-will melodramatics substitute for the usual B-Western shootin' and fightin' in this late entry in the long running Hopalong Cassidy series, which has sidekick California Carlson (Andy Clyde) as one of six heirs to the supposedly worthless Baxter property. During the reading of Hiram Baxter's will, one of the heirs, Phineas Phipps (Joel Friedkin), is murdered, presumably by the same mystery figure who had earlier taken pot shots of the arriving Hoppy (William Boyd), Lucky (Rand Brooks), and California. Soon panels are sliding, spectral voices are heard, and shots are fired. Yet another heir, Ralph Baxter (Nedrick Young), is murdered and crooked attorney Potter (John Parrish) points the finger at Lucky. Meanwhile, Hoppy discovers that there is oil in them thar hills, a fact that Potter and co-conspirator Ogden (Robert B. Williams) conveniently forgot to mention to the heirs. After performing a bit of detective work, Hoppy catches the mystery killer in the act, so to speak, and the ranch is eventually returned to the surviving heirs, Ruth Baxter (Patricia Tate), housekeeper Mathilda Hackett (Una O'Connor), ranch hand Joshua Colter (Earle Hodgins), and California. The latter, however, relinquishes his share in favor of returning to the Bar 20 with his friends.