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.

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.

The guys land in Baltimore on February 22, 1861, in a barn where a group of conspirators and followers of Abolitionist John Brown are meeting. They are mistaken for fellow collaborators, but the Pinkertons break up the meeting. Doug is captured while Tony escapes with brothers Jeremiah and Matthew. They still plan to blow up Lincoln, who is enroute to his inauguration. While Doug tries to convince Pinkerton he is innocent, Tony tries to persuade the brothers not to go through with there plan, but Jeremiah is determined. Tony manages to escape but Pinkerton doesn't believe him either. The two manage to convince Pinkerton there is a bomb and go to look for it. The Project staff have spotted the bomb and brought it to the future to disarm it, accidentally scooping up the conspirators' other, younger brother David. They convince David to delay the bomb before having to send him and the bomb back. As Lincoln departs, Tony, Doug, and brother Matthew manage to convince Jeremiah that his cause

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 on an island in the South Pacific at the tail end of WW2. Two Japanese soldiers are holding it against invasion: the deranged Lt. Nakamura, who hates Americans, and the loyal sergeant, Itsugi. Nakamura soon fixates on the travellers, and forces them into a series of sadistic games. When the Project: TickTock staff call in a consultant to try and get a fix on the guys' location, the consultant turns out to be the lieutenant's father. Apparently Nakamura disappeared during the War and now his father wants them to recover his son. Tony and Doug manage to turn the tables on Nakamura and warn the advancing fleet. The young Nakamura, a failed kamikaze pilot, finally decides to end his life with honor by seppuku, as his father looks on through the portal.

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.

Arriving in Gettysburg in the 1860's, Doug and Tony are separated by an explosion which seemingly gives Tony. A jolt from the Tunnel revives him but with amnesia. Doug falls in with the Union forces, while Tony becomes involved with the South and Sgt. Maddox when he is mistaken as a courier sent to buy gunpowder from an arms merchant, Michaels, who stole the stuff from the Union. Doug gets there first to find the merchant is Machiavelli! Apparently Machiavelli's pattern matches Tony's, and he was swept up and brought to Gettysburg by the Time Tunnel. The Tunnel send Machiavelli's dog back when it's about to kill Doug, draining them of power.

The amnesiac Tony takes Doug prisoner and turns him over to his sergeant, while Machiavelli delights in the carnage. Doug escapes and tries to save Tony who is determined to complete his mission. Machiavelli kills Maddox and then Doug and Tony fight when Doug tries to destroy the gunpowder. The two men come to terms but when Machiavelli tries to de

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