Dr. Tony Newman prematurely enters the government's Time Tunnel project, and the project head, Doug Phillips, must go back to save him as they both fight for survival on the sinking Titanic.

Doug and Tony land 10 years in the future on the Mars Excursion Module during liftoff. Their extra 335 pounds of weight endanger the mission by putting it over the weight allowance. Everyone believes the time travellers are spies except one man, Harlow. They are forced to land on the moon for a refueling stop, but the ship crashes. One of the other men, Beard, kills Harlow. Beard is a spy. To further confuse matters, ten years in the past at Project TicToc, Beard and another spy, Brandon, are visiting the complex. Brandon sabotages the tunnel and then tries to escape, but Beard shoots his superior to bolster his own cover and his own role remains undiscovered. In the future, Doug and Tony manage to blow up the ""future"" Beard, but the MEM takes off without them. As they are stranded on the moon, their air running out, the Tunnel scoops them up and sends them on their way. (Copyright 2003 Steve Crow)

Dony and Toug arrive in 1910, where a local town is in a panic over the arrival of Halley's Comet. Tony is caught in a cave-in near two hundred miners, while Doug is unable to get help from the superintendent, Henderson, who believes they're all doomed because of the comet. Doug digs out Tony on his own, and tries to convince the local astronomer, Ainsley, who has everyone in a panic. While Tony tries to set up a rescue, the Project team try to send Doug a radioscope through the Tunnel. That plan fails, but Doug makes a primitive radioscope and shows Ainsley the gravitational forces that will cause Halley's Comet to deviate. Ainsley convinces the townspeople they are not doomed, and everyone teams up to rescue the miners. Meanwhile the Tunnel sucks in Halley's Comet and the power flow almost sucks Jerry into the Tunnel before they can cut pull the plug.

Tony and Doug arrive at the Siege of Troy, and are taken before Ulysses. Ulysses believes them to be gods, while his lieutenant Sardis doubts them. Doug wins a swordfight with Sardis to prove his divinity, so Sardis goes to Troy and tries to betray Ulysses and the Greeks. In the next battle the two travellers are almost overwhelmed, so the Project scientists send back Jiggs with a bag of hand grenades. Doug is captured during the next battle and put on the rack to be tortured. Jiggs is returned, but ages horrendously while trapped in the infinity of the Tunnel. The scientists manage to reverse the effects, but accidentally pull a Greek soldier forward (they manage to send him back). Tony ""inspires"" Ulysses to create the Trojan Horse, and goes inside it to rescue Doug. The ploy is successful. Ulysses kills Paris and rescues Helen, while Tony rescues Doug and the two vanish before the astounded Greeks.

The guys arrive in Arizona, 1547, as a technician named Niman kills a scientist. After a shootout, he flees into the Tunnel. Niman is a spy who has planted a nuclear device in the complex. The guys need to find Niman to get him to reveal the location of the bomb. They lure him in with a fire but he slips, and the Project transfer Doug and Tony after him to 1,000,000 A.D. Niman is already there and has established himself with the ruling clique. The guys get the info on the detonation time, bypass a force field, and with the aid of a local female ""defective"" manage to get to Niman. The Project transfers everyone, including two of the future-types, back to 1,000,000 B.C. After some running around from dinosaurs, they rescue Niman from a quicksand pit in return for the location of the bomb. The head alien eventually comes around and forces Niman to give the location of the bomb which they defuse. Everyone ends up in a giant bee hive and the Project gets everyone but Niman out.