Tom, a U.S. Intelligence maintenance staff member, was accidentally miniaturized to three inches tall alongside his assistant, Swingin' Jack. The accident occurred when he fell near experimental equipment, activating a shrinking laser ray gun. This miniaturization appears permanent. In response, Tom founded the Tiny Human Underground Military Bureau (T.H.U.M.B.) to leverage their reduced size for intelligence work, serving as its primary field agent.

T.H.U.M.B. operates from a repurposed file cabinet drawer within U.S. Intelligence headquarters, functioning as both living quarters and operational base. They employ miniature vehicles and equipment, including a two-man helicopter and a jet fighter plane, likely shrunk during the same accident, for missions. The organization tackles assignments impossible for normal-sized personnel, exploiting scenarios where small size offers a tactical edge. Tom reports directly to Chief Homer J. Chief, an irritable intelligence officer who assigns missions targeting threats from M.A.D. (Maladjusted, Anti-social, and Darn mean).

During missions, Tom exhibits persistent eagerness and confidence, frequently using catchphrases like "Can't win them all, Chief Chief" and "On the ball and ready for action!". Operational successes typically stem more from fortunate coincidences than deliberate skill, partly due to Swingin' Jack's frequent operational errors complicating objectives. Their mission parameters involve neutralizing diverse M.A.D. threats. These include retrieving secret weapon plans from sunken vessels, disarming subterranean world-destroying devices through narrow access points, investigating unexplained military aircraft losses, countering attempts to steal Earth's oceans, preventing landmark theft via reverse polarization technology, and neutralizing mechanical viruses inducing disruptive dances. M.A.D. operatives, identifiable by black hats and trenchcoats, pursue globally destructive schemes for unspecified personal gain.

Mission profiles and character dynamics remain consistent throughout documented assignments, focusing on countering M.A.D. plots through size-based infiltration and disruption tactics without major alterations to operational methodology.