Congress has poured seven billion dollars into a large and deep hole in the ground - the home of Project TicToc and its revolutionary new technology, the Time Tunnel. A mechanism intended to access past and future, the tunnel is not quite ready despite a decade of work and all the billions. Senator Clark declares his intention to cut funding and abandon the project. Desperate scientist Tony Newman uses the apparatus to send himself through time to prove the concept. But the TicToc team cannot retrieve him, and so his mentor Doug Phillips goes back to help Tony out of the peril he has landed in: he has arrived on the RMS Titanic the day before she struck an iceberg and sank.
Doug and Tony escape death aboard the Titanic only to be hurled ten years into their future aboard a rocket bound for the moon. Problems arise which the astronauts blame on their unwilling stowaways, but the real cause is a saboteur aboard the flight - and the same man, ten years earlier, is in the TicToc complex with a confederate! Doug and Tony must discover the identity of the traitor and stop his plans or else die in space.
Doug and Tony arrive in a mine shaft in 1910, the year that Halley's Comet passes close to earth. Many fear it as a supernatural event. A local scientist calculates it will strike nearby. A collapse has Doug and Tony trying to save lives.
Doug and Tony are transported to New Orleans where Tony steals two buckskins for them to wear. They are captured by the British Seventh Royal Regiment commanded by Colonel 'The Butcher' Southall. They find themselves behind the British lines in the War of 1812 against the United Kingdom where they are mistakenly taken to be spies. They go to a partial court martial and sentenced to be executed by firing squad by The Butcher. Furthermore they realize that the day is 07 January 1815, the eve of the ultimate attack of Colonel Southall against the strongest side of Commander Andrew Jackson's defenses, when the British officer led his men to a slaughter. Meanwhile General Kirk invites the British General Phillip Southall, who is a descendant of The Butcher, to visit The Time Tunnel facility to feed the personnel with information about his ancestor.
Tony and Doug are transported to Krakatoa, a volcanic island between Java and Sumatra in great activity, and the blowup seems to be imminent. The travelers in time are attacked by superstitious natives who believe that a sacrifice would appease the fire, but they are rescued by the British Dr. Everett Holland, who is researching the volcano with his daughter Eve. They ask the date, and the Hollands say that it is 26 August 1883, the eve of the explosive eruption that destroyed the island, encircled the globe with ash, and caused a tsunami that killed more than 36,000 people. Tony and Doug try to convince the Hollands to leave Krakatoa, but the distrustful Eve believes that they are American scientists interested in stealing her father's research. Meanwhile, the Time Tunnel personnel bring Tony back to the facility, but a time warp suspend the passage of time and the personnel are frozen. Tony collects information about the blowup in Krakatoa and returns to the island, leaving a message for Dr. Raymond Swain. When General Kirk succeeds in contacting Tony, Eve overhears the conversation, and Tony confesses that Doug and he are travelers in time. But they realize that there is a mistake in the date, and now it may be too late to leave Krakatoa.
Doug and Tony are in 1200 BC during the war between Greeks and Trojans. They are captured by Ulysses and their knowledge of history makes him think they are gods. Doug is captured by traitor Sardis, brought to Troy and meets Helen of Troy.
Doug and Tony are transported to the summer of 1876 and witness soldiers slaughtered by Indians in the middle of the desert. They are hunted and captured by three Indians; however Doug is rescued by the Trumpeter Tim that survived the massacre and is bringing a dispatch from General Crook to General George Armstrong Custer. Doug escapes but the leader of the Indians, Crazy Horse, brings Tony to the Indian camp to get information about the "Yellow Hair". Meanwhile, the Time Tunnel personnel summon the specialist in the Indian Wars period and Sioux descendent Dr. Charles Whitebird to provide information about the location. The researcher advises that the place is Montana and the day is the eve of the day of The Battle of the Little Bighorn, where Custer and the 7th Cavalry Regiment where defeated and annihilated by the Indians led by Sitting Bull.
At the French penal colony of Devil's Island in 1895, where prisoners were sent and never left, Doug and Tony are mistaken as runaway prisoners. They try to tell the prisoners their plan to help Captain Alfred Dreyfus escape is doomed.
The guys are transported to 1956 Russia and receive a message from the Time Tunnel: "Meet Alexis". They meet the agent who gets them to a Soviet Time Tunnel he is in charge of and insists they pilot the craft. They know its doomed future.
The guys are transported to February 1861 to a barn where a group of conspirators led by Jeremiah plots to kill Abraham Lincoln. They have developed a time bomb but are surprised by a raid of governmental agents. Tony flees with Jeremiah.
Doug and Tony are transported to 1836 and are immediately attacked by Mexican soldiers. The nearest shelter turns out to be the Alamo days before the Mexican Army will overrun it. Colonel Travis decides they are spies and imprisons them.
Doug and Tony land in nineteenth century Asia, meet Rudyard Kipling and become involved in the conflict between the British and local tribesman for control of the Khyber Pass.
Landing in 1944 Nazi-occupied France two days before D-Day, Doug is captured by the Gestapo and psychologically reprogrammed to hunt down and kill Tony, who must keep secret their knowledge concerning the imminent Allied invasion.
In thirteenth century England, Doug and Tony become involved with the Earl of Huntington otherwise known as the legendary Robin Hood and their efforts to get King John to sign the Magna Carta.
On a Pacific isle about to be bombed by America, Doug and Tony are held by a downed Japanese pilot and a sergeant. Kirk brings in a Japanese officer who served on the island. He won't help unless they save his son who died during the war.
Doug and Tony are transported to a spacecraft with two weird aliens that intend to invade Earth to steal proteins for their dying planet. They land on Mullins, Arizona, in 1885, and the aliens use a device called "Projector" to subdue the earthlings. The time travelers decide to resist the invasion to save Earth from the eminent destruction, but the powerful aliens seem to be unbeatable.
During an encounter between the Germans and the Italians in World War I, Doug and Tony land in a villa that is haunted by the ghost of the Roman Emperor Nero.
Doug and Tony land in 1519 Mexico, where Cortez is looking for a golden mask. Their archaeology expert back at the Time Tunnel insists that they retrieve the mask, which he has been searching for for twenty years, or he will not help them.
Landing in 1881 New Mexico in the middle of a jailbreak of Billy the Kid, to defend Tony Doug shoots at Billy who escapes swearing to hunt down Doug. According to their research back at the Time Tunnel, two unknown strangers were killed by him on that date.
Doug and Tony have a run-in with pirates off the Barbary Coast in 1805 and help in the rescue of the nephew of the King of Spain assisted by American Naval officer Stephane Decatur.
A saboteur enters the Time Tunnel HQ and kills Dr. Stiles, plants a timed nuclear bomb, exits through the tunnel and ends up with the guys. The tunnel sends the trio one million years ahead. They encounter two humanoids from the future.
Ending up on different sides just prior to the Battle of Gettysburg, Doug and Tony must stop an attempt by Machiavelli (who had traveled in time from the Renaissance due to the Time Tunnel Project) from trying to affect the outcome of the battle and send him back into time.
Doug and Tony must help Marco Polo stop an attack by Mongols in thirteenth century China. Tony meets and falls in love with the daughter of Kubla Kahn.
During the Battle of Khartoum in 1883, Tony and Doug stumble upon aliens who plan to conquer the Earth using missiles. The aliens also send a bomb through the Time Tunnel to prevent any interference with their plans.