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.

On the island of Krakatoa in 1883, time travelers Doug and Tony try to convince a British scientist that the volcano is about to erupt in one of history's biggest explosions.

The guys arrive in Paris, 1793, and Doug is arrested by the Committee for Public Safety. Tony rescues him with the aid of a shopkeeper, who is a royalist and friend of Marie Antoinette. Meanwhile, Kirk has the Project send back an irradiated personal ring to the guys which they hope will act as a focal point to home in on. Doug and Tony get the ring, but then reveal themselves to a man who is a splitting image of General Kirk! This General, Querque, is with the Revolution and has them arrested, along with the shopkeeper. Querque has the ring and believes it is the evidence he needs to have Antoinette executed. Kirk brings his ancestor into the present and tries to convince him to change his mind. Querque escapes back into the Tunnel when they send the ring back, and tries to thwart Doug and Tony. They escape, and with forged passports get to Marie Antoinette and then help the Dauphin to escape. The shopkeeper and the Dauphin get on board a departing ship: Tony recognizes the Corsican g

Tony is shot by Afghani tribesmen and left for dead, and they then take Doug prisoner. Doug is taken before Singh, the head of the Afghanis fighting against the British in 1876, while Rudyard Kipling rescues Tony and takes him to the English fort. The Afghanis are preparing for a massive attack on the English, the 'Night of the Long Knives'. With the aid of a blind slave, Doug escapes and gets back to the fort, while Kipling is captured. The general in charge has been ordered to only defend himself, so he has the head of the Afghani forces under English command launch an ""unofficial"" attack. Doug and Tony accompany them and rescue Kipling, and Singh is killed in the attack.

Doug and Tony arrive in Lincoln in late April in the 1860s, and run afoul of Billy the Kid. Doug shoots Billy and apparently kills him, then he and Tony escapes. It turns out Billy took the bullet in the belt buckle, and he goes after the two. They manage to capture him thanks to a voice-transmitted distraction provided by Kirk, but Tony goes back into town and is mistaken for Billy. Pat Garrett arrives and eventually convinces the sheriff that Tony isn't Billy, but the mob isn't hearing it. Billy catches up to Doug and challenges him to a gunfight. Pat and Tony get involved, with Tony knocking out one of Billy's men planning to backshoot Doug and Pat intervening when Doug blows it. The two men are whisked off again.

Tony and Doug are frozen in time, then a rather fey Merlin appears in the Project base. He takes the guys out of time and freezes them, commands them to do his bidding, then sends them on to 544 A.D., Cornwall England. They meet a young pre-King Arthur while fighting Vikings and on Merlin's behest team up with Arthur. The Vikings apparently kill Doug and capture Tony and Arthur. Tony escapes with Arthur and Doug is rescued by Merlin and Guienvere. When the Project staff are ready to recover Doug and Tony, Merlin intervenes because he needs them where they are. Tony and Arthur get recaptured and so does Doug when he goes to help. Guinevere gets captured too. One of the Vikings kills Arthur and a ""detained"" Merlin shows up and reverses time to save him. The guys escape again and Doug gets reinforcements which Merlin disguises as Vikings while Arthur and Tony rescue Guinevere. Everything works out and Arthur and Guinevere are to be married.

The guys' signal is intercepted and a silver-skinned alien shows up and kidnaps Anne. He leaves behind a data card which the rest of the Project staff use to send Tony and Doug to. The guys end up in a futuristic complex and meet a zombiefied ancients from different time periods and locales. A mysterious voice provides historical detail. According to the Project staff they're on a distant planet in the Canopis system in 8433 A.D. The guys meet the Curator then escape. They get hold of Ann before being captured and the Project staff try a recovery but grab a OTT (""Official Time Traveller) instead. He grabs the Time Tunnel's time/space converter and leaves. The guys and Ann stage an escape but mess that up as well. The Canopians go dormant during night, and the guys avoid being drugged to take advantage of the situation. They get nowhere for a while, and the OTT is not vulnerable to lack of sunlight. The three Earthlings manage to overcome it long enough to send Ann back with the convert