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 land in the War of 1812 in Louisiana, and steal som clothing that happens to have passes from General Jackson. They are captured by the British forces, led by Colonel Southall. In the present, the Project people bring in Southalll's descendent, a British general. His ancestor has a reputation as a butcher by sending his men into the strongest flank of the American forces. In the past, Col. Southall forces Tony to lead one of his men to the enemy lines, get a report, and send up a signal rocket of which flank he should attack. Tony and the scout get captured, escape, and prepare to send the signal. Meanwhile, General Southall insists on returning to the past. He's dying of cancer, and Kirk reluctantly grants the general, an old friend, his last request. The present Southall helps Doug escape and then confronts his ancestor and manages to convince him he is from the future. Doug helps Tony but the signal rocket goes astray and the attacking British are wiped out. General So

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 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

Doug and Tony arrive in Russia in 1956. The Tunnel staff try to contact them with F-5 probes, which prove highly dangerous. In the last probe the team sends a message telling the guys to contact ""Alexis"", pose as defecting scientists, and find out about Project A-13. In the present-day, General Parker is dealing with a scientist named Biraki and wants to know what his connection is. The guys are lead to the project in 1956, where Biraki is working on a Time Tunnel for the Russians under the supervision of Hruda. Doug determines the project is doomed to fail, and they try to escape and are recaptured. They also find out that Alexis is a double-agent. With some help from the Tunnel team, the guys manage to survive the probe, then sabotage Biraki's project in the past. The Tick-Tock staff witness the whole thing and tell Parker that Biraki is trying to get revenge for the destruciton of his Tunnel in '56, then manage to transfer Doug and Tony to another time period after they escape.

Tony and Doug arrive at the Alamo on March 6, 1836 - the day Santa Ana wiped out the defenders. The two make it to the fort, but are put into custody when Tony tries to convince the stubborn Col. Travis the fort is doomed. Tony escapes but is captured by the Mexicans. An injured Doug captures Capt. Reynerson and tries to convince him he can see the future. When Col. Travis is killed in a fall during Tony's escape as Doug predicted, Reynerson believes him. Tony manages to escape the Mexicans with the help of a sympathetic Dr. Armandez. Meanwhile, the project team have been trying to stage a recovery, but grab Col. Travis by mistake. He is stunned, but Kirk eventually convinces him by showing him future-footage of the battle, and Travis' own death. Convinced that he must let Doug go before the massacre begins, Travis returns and frees him. The Alamo defenders are gunned down, and Tony and Doug reunite. With Armandez' aid they get Reynerson's wife out before they are whisked away.

Doug and Tony are captured by the Gestapo in Cherbourg on June 4, 1944, two days before D-Day. A scientist, Dr. Heinz Kleinemann, working for the Reich plans to brainwash Doug and allows Tony to escape. Tony falls in with the Resistance while Kleinemann successfully brainwashes Doug to beleive he is 'Heinrich Kriegler', whose father was killed by Tony. The Resistance cell is suspicious of Tony but need his electronic knowledge. Doug tries to kill Tony but Tony escapes, although the attempt further arouses the Resistance's suspicions. Tony is forced to shoot Doug later, and takes him captive. Doug reveals a traitor within the cell, and then they launch an attack on the Gestapo HQ and recover Kleinemann and the serum they need to restore Doug to normal. They succeed, and Kleinemann restores Doug's identity. The Resistance take Kleinemann into custody and Tony and Doug are whisked away as the bombing begins.

The guys land in a Western town in the late 19th century, where they are intercepted by two silver-clad aliens. The two aliens need to steal protein to supplement their own supplies, and soon use their advanced technology to mind-control Doug and hold the confused townspeople at bay while stealing local cattle. Tony manages to get hold of one of the alien control devices. Meanwhile, at Project TickTock the same alien race but from 1966 arrive and demand to know what happened to their scouting party a hundred years earlier, believing the Project to have something to do with it. Tony manages to free Doug from mind control and defeat the aliens in the past, while the ones in the present witness the departure of the scouting party in the past and are satisfied Earth had nothing to do with their disappearance.

Tony and Doug arrive near the Italian-Austrian Alps on October 23, 1915, as the Germans are preparing to bombard the area. An explosion knocks them out and uncovers the stone coffin of Emperor Nero. Nero's sword floats out of it, but kills a German soldier. They awaken and discover they are beneath the villa of Count Galba. He claims the two travelers are American friends, covering for them against the invading Germans. The ghost of Nero has other ideas, and wants to kill Galba, whose ancestor was responsible for Nero's death. First a German soldier then Tony are possessed by the ghost. The Time Tunnel project staff manage to free Tony with a high-powered electrical discharge on the recommendation of a Dr. Steinholtz, whom they call in. However, they then pull the ghost into the current day, but manage to send him back. Tony and Doug get Galba to safety and help lead the Italian resistance to the Germans. The German leader, Neistadt, flees but Nero's ghost delays him long enough for an

Doug and Tony arrive in a jungle in 1519 Yucatan as Cortez and his Spanish conquistadores attack the locals. The pair rescue natives being tortured for knowledge of a sacred golden mask and intervene. They are captured and believed to be spies. Cortez burns his ships and plans the guys' execution, but one of the locals free them and Doug buys them time to escape by threatening Cortez with explosives. Cortez orders pursuit. Meanwhile, the Project team call up an expert familiar with the terrain, Castillano. The guys use crude explosives to delay the Spaniards while aiding a local chieftain-to-be, while the Project staff discovers Castillano has a reputation for stealing artifacts, but have no choice but to employ him. When the guys get captured Castillano offers the Project staff their location in return for the recovery of the mask. When the Staff recover the mask they inadvertently lock everyone in time, and Castillano grabs a gun to force them to let him keep the mask. A demented Cas

Doug and Tony arrive on the Spanish Main on April 1805, where they are captured by Captain Beal and his crew. They befriend Armando, a young boy who claims to be the nephew of the King of Spain. Tony eventually manages to escape where he is found by the attacking British who are unwilling to try and help Doug and Armando. Beal tries to kill Doug but is whisked back to Project Tick-Tock. He takes Anne hostage but eventually goes back into the Tunnel and his own time. The Project staff use the Tunnel to whisk Doug and Armando out of trouble after Beal is killed by his henchman. However, the two are caught in a bombardment and seriously wounded. A doctor friend of Kirk's due for retirement, Berkhart, volunteers to go back despite the fact he has no chance of being returned. He saves Doug and Armando before the travellers are whisked away.

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.

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