"Scrat, the saber-toothed squirrel (a fictional animal from the Ice Age film series), while trying to find a place to hide his acorn, digs up a buried time machine over an ice-encased skeletal body of a human time traveler. The machine activates, stating the date that Scrat is in (May 26, One Million B.C.) While sniffing around the machine, he accidentally presses a button on it, and the machine powers up and then zaps the acorn. Scrat gets mad and tries to beat up the time machine, but it zaps him too, sending him to the Middle Ages in 1250 AD, where he finds the acorn wedged under a rock. Scrat sees Excalibur, the sword in the stone, and decides to use it to move the rock and get back his acorn. He pulls out the sword but then finds himself under attack by a group of unseen Robin Hood archers, and uses the sword to block the arrows fired by the archers. He inadvertently frees the acorn in the process (and gets his tail wedged in the rock and having to yank it free) and takes it and the time machine and races off to find cover, only to hide in the barrel of a lit cannon. The cannon fires him into the path of hundreds of incoming arrows. The time machine zaps the acorn mid-flight and Scrat narrowly manages to activate the machine again for himself.

He materializes in the Coliseum during Ancient Rome. Scrat reaches for his acorn, but is dragged off when his tail is caught by a passing horse-drawn chariot. Scrat tries to pull his tail off, and begins to enjoy the ride (as he is "laughing" as the chariot pulls him) just as his crotch bashes against a rock. He then finds his acorn just as a fanfare sounds. He thinks it is victory music and introduces himself to the crowd like a triumphant gladiator, proudly holding up his acorn. Then he hears the growl of a lion coming from the tunnel behind him. He fires the time machine again before the lion can attack him, and lands on an ice field. He is overjoyed, thinking he is home, but he soon sees the ill-fated RMS Titanic appear out of nowhere, heading straight towards him; he was actually in April 14, 1912 A.D. and on the frozen North Atlantic, the time and location of the ship's sinking. Scrat gets pressed into the iceberg that sank the Titanic by the ship's bow, and the time machine zaps Scrat and the acorn as they fall from the iceberg, taking Scrat to the time of the first Ice Age movie, where he encounters his past self, and the two Scrats fights each other for the acorn (Manny, Sid, Diego, and Roshan are watching the fight going on). The time machine is caught in the fight, and it zaps the acorn out of sight yet again, much to the distress of both past Scrat and future Scrat. Shortly after, future Scrat also gets zapped (after past Scrat angrily kicks the machine).

Scrat is then sent to many dangerous situations where he would have been killed had he not activated the time machine in time; under a launching Saturn V rocket during the Space Race, in a dark, modern-day jewelry store (he sets off the security alarms and lasers when he picks up a diamond he mistakes for his acorn), in a girl's locker room in the present (where he is hit by a roller brush), in the French Revolution (where he appears under the falling blade of a guillotine), during Benjamin Franklin's kite flying experiment (and almost gets electrocuted), in front of a wrecking ball demolishing a modern-looking building, in front of the Hiroshima bombing during World War II, on the tracks of an oncoming train in the Wild West, and in front of the groin of Michelangelo's David (this doesn't threaten him, but he is rather embarrassed). Frustrated, Scrat punches the machine, which sends him into a strange dimension (possibly a time vortex) of floating musical instruments from the orchestra. Scrat spots his acorn but gets hit split into clones by a clock and grabs it just before being drawn into a wormhole along with his acorn and the time machine.

The wormhole lands Scrat in front of an enormous oak tree. Overjoyed at the sight of so many acorns, he tosses away his own acorn, which lands on and almost causes the time machine to fire again, but not before Scrat pulverizes it. Scrat attempts to remove the nuts from the tree, but soon discovers that it is only a monument of some sort, with a plaque on it reading "Here Stood the Last Oak Tree". Scrat is in the distant future in the year 200,000 AD, where oak trees (and therefore acorns) are extinct and have all gone away. He realizes that the acorn he brought with him is the only real one around. He makes a dash for it, but the time machine somehow fires one final time, transporting the acorn right out of his paws right before the time machine collapses into pieces. Stranded in the acorn-less future, Scrat lets out a scream of frustration, ending the film. The forever-lost acorn ends up floating behind the credits."