Colin Limmerick is faced with the continuing dilemma of time travel gone wrong. Prehistoric beasts have filtered through the vortex of time and have appeared in his present day of 1910. Rosa, his past love, indicates they must block the passage of time and the only way to do it is to venture through another prehistoric journey.
The eccentric Russian scientist, Dr. Sasha Dimitrikov, who developed the time travel device explains their return trip through time may not take them to the days prehistoric beasts roamed, but they could land anywhere in time.
Limmerick has misgivings about his prehistoric expeditions through time, he feels he has opened a Pandora's Box by trying to play God. His life grows even more chaotic when he finds himself in the chancellor's bed. The chancellor agrees to fund his prehistoric time travels if he agrees to be her lover. He breaks his engagement with Amoli, who tries desperately to win him back.
When they enter the time vortex, they, by mistake end up in 840A.D., the time of the ancient Celts. Viking invasions are ravaging Celtic villages and they are not prepared for this time in history. He is chosen to be the head warrior for the Celts in a series of battles with Viking warriors. He is unsure of himself because of his lack of experience with a sword. Dr. Dimitrikov tries to teach him swordsmanship, but it takes years for a great warrior to master a sword. When the head Chieftain of the Celts, first sees Amoli, her beauty enchants him; where he must have her. He demands to fight Limmerick to the death for Amoli's hand. The battle intensifies, while the spectators are roar with terror, thinking their newfound Celtic warrior has been killed by the Chieftain.
Rosa is jumped by two Celtic hunters, she fights them off but they manage to steal Dr. Dimitrikov's time travel device. Despite all he has been through, she is determined to come up with a plan to retrieve the very important time travel device. There are also continuous meetings with Megaloceros giganteus; a prehistoric beast that leaked through the passage of time and ended up in the time of the ancient Celts.
The Celts set up a burial for Limmerick. Rosa tries desperately to reach him. She kneels by his side to realize that he miraculously survived the battle. Amoli becomes the Chieftain's possession, but when he sees Limmerick is alive, he refuses to give her up. Limmerick and Dimitrikov both charge at the Chieftain with two-handed claymores and relentlessly fight him to his death.
Dr. Dimitrikov finally positions the time travel device to take them back to 1910 A.D. They return to their modern-day living but Colin Limmerick is distraught that they witnessed a prehistoric mammal roaming an ancient Celtic time period. He realizes that he is an ill-prepared time traveler but learns through this Celtic Odyssey that prehistoric beasts are roaming throughout time.
