During a fierce thunderstorm, Sky picks up a mayday call from a Air Force courier plane which is about to run out of gas. The Air Force request Sky's assistance in locating the downed aircraft because the pilot is transporting secret documents that are of interest to foreign governments. Sky locates the plane wreck, but the pilot is nowhere to be found. When he discovers that the navigational instruments have been tampered with, Sky fears that enemy agents may have located and stolen the secret plans and are headed for the nearby Mexican border.

When Penny discovers a wounded carrier pigeon carrying a valuable ruby attached to its leg, Sky suspects a gang of jewel smugglers is operating in the area. With the help of a Mexican police detective, Sky sets up to break up the criminal operation.

A crooked express agent fakes a hold-up to steal gold from his company's vault. He uses an old stagecoach to get the stolen loot out of town.

While helping a friend run his freight airline after an accident, Sky stumbles across a gold-smuggling operation.

Sky's efforts to prove corruption in the county clerk's office nearly result in disaster, when Sky's foreman, a non-pilot, must land the Songbird when Clipper becomes too ill to fly the plane.

Sky becomes suspicious when a Eastern woman shows up in Grover claiming to be the long-lost niece and heir of a dead rancher.

Penny picks up the wrong suitcase at the airport and discovers it's full of counterfeit money. Sky suspects that a young former engraver might be involved.

A rancher disinherits his nephew in favor of his young son. When the rancher is murdered the young man is blamed. Sky hopes that by faking a jailbreak, the real murderer will be forced into the open, but the plan backfires when Clipper and the young man are kidnapped.

Sky King picks up a young hitchhiker who refuses to divulge his identity, or where he's been or going. Determined to fill in the blank spaces on the young man's resume, Sky learns that he is an escapee from a boy's reformatory who was involved in a recent bank robbery.

A young rancher disappears after the man attempting to foreclose on his mortgage is murdered. Sky is convinced that the man is innocent and that there's another explanation for the man's apparent flight.

Eastern gangsters set up a protection racket near Grover and the local ranchers appeal to Sky for help.

The drug Sky delivers to a critically ill man does more than save his life; the medicine causes the man to confess that he's a former criminal who has attempted to go straight.

Angry that Sky and Clipper won't allow her to join the search for a missing refugee professor, Penny slaps on a pair of six-shooters and launches her own investigation.

Penny sees a man escape from a doctor's office, and is informed that the man is a dangerous mental patient. Sky looks into the incident, and soon finds himself mixed up in foreign spies and poison gas.

Sky investigates a series of mysterious payroll robberies, where the police chase the robbers only to see their getaway car mysteriously disappear.

A couple of Easterners claim to have traveled west to visit a dude ranch, but are actually a pair of con artists willing to commit murder to obtain a ranch with a rich uranium deposit on it.

Sky teams up with a military intelligence officer to track down a foreign agent who blew up a secret government project.

Sky stumbles across a dead pilot and suspicious looking plane wreck and discovers that the man was murdered and the crash never happened. He learns that the plane was carrying a number of valuable pieces of ancient Chinese art, all of which are missing from the plane's cargo hold.