There's plenty of light moments in this show, such as Hoss' amazement and Jamie's curiousity at how a camera works; kindhearted photographer Sam Dawson's interaction with both; and a snobbish Mrs. Olesen-type woman who schemes for the spotlight by requesting to sit in a prime seat on-stage.
But the prime focus of "Terror at 2:00" is on a white supremacist named Mr. Ganz, whose hatred of Native Americans runs so deep and is so personal he plans to interrupt a peace treaty signing between a Paiute tribe and the U.S. Army, one that Ben helped mete out, with the ultimate goal of a war that will eventually lead the Indians' genocide.
In the show's opening act, Ganz and his henchmen kill two Army soldiers who are transporting a Gatling gun, an advanced weapon (for the post-Civil War era) which can fire off 600 rounds a minute. The plot involves massacring everyone – the Cartwrights, the Indians, onlookers and others who just plan to celebrate – who are on hand to witness the treaty signing.
The bad guys confiscate the Gatling gun and travel to Virginia City, where the treaty is being signed. The group pose as reporters and photographers with the St. Louis Daily Record, assigned to cover the treaty signing. In boxes marked "camera equipment," they smuggle the weapon into a hotel room overlooking the street.
Ganz can't wait for 2 p.m., the scheduled time of the treaty singing. He stares into a pendulum clock and recalls his own experience with Indians. Always having hated the redman, his own son once fell in love with a Paiute squaw and the two married with her father's blessing. Once Ganz found out, he murdered his son.
The memory only fuels his hatred and his desire to wipe out all Native Americans. He surmises that word of the massacre will spread, both sides will blame the other and another Indian war will break out. Eventually, after all Paiutes are killed, then the Utes, Sioux, Cherokees, and so on until all red men are exterminated. He doesn't care how many white men are killed, just so long as his goal is met.
Sam, intrigued by the "reporters" and their profession, visits with Ganz about his experiences, but once he sees the gun and realizes who Ganz really is, he is taken hostage. Hoss, who goes checks on what is keeping Sam, is also quickly subdued by the bad guys. Ganz reveals his plan and plans to force Hoss to watch (Sam had been knocked out).
Two o'clock quickly approaches and it appears Ganz's extermination plan will come together--until Joe wonders what is keeping Hoss. He and Clem see the buckboard that Graham (one of the "reporters") borrowed from the Cartwrigths parked outside a side door to the hotel and they go investigate.
Joe begins to ask for the buggy back, but Graham reveals a gun. He disarms Joe and Clem and plans to lead them both inside the hotel room where Ganz is, but Joe manages to smash the door into the bad guy. Clem takes Graham into custody and Joe races to the hotel room.
Once Joe calls into the hotel room, Hoss manages to subdue Hunter as Ganz prepares the Gatling gun to blow Joe away once he enters. However, Joe is too agile; as Ganz is reloading, Joe guns him down and averts tragedy.
Ben, the Army and the Paiutes arrive in Virginia City, five minutes late, oblivious to what had just happened.