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 Japanese Consulate in Honolulu on December 6, 1941, and see three men burning files. They talk their way out and Tony goes to find his father, who disappeared during the bombing. Cmdr. Newman is initially skeptical, but Tony convinces him with family knowledge no one else could know. The Japanese agents get wind of Tony and Doug's knowledge, capture the pair, and interrogate them for information. They don't break, and manage to escape. Meanwhile, Cmdr. Newman is at Naval HQ checking out Tony's warning, and the Project staff realize that if the young Tony (who was also present at Pearl Harbor) isn't rescued, then ""their"" Tony will vanish. Tony manages to convince the housekeeper, Mrs. Neal, to flee to the mountains with her child and Tony, and then he goes to rescue his father. They head to Naval HQ but a barrage hits and Cmdr. Newman is killed. An unexploded bomb lands, and the Project staff use the Tunnel to delay it long enough for the travellers to get clea

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.

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.