In a 1960s-style Mexican laboratory, the Spanish professor shows his assistant, Daffy Duck, his newely-created time machine. He asks Daffy to watch it while he naps, and warns him a couple of times to not pull the chain. Suddenly, Daffy hears Speedy Gonzales and his mariachi mice band play right outside the lab. This annoys him, so he tries to silence him with a broom, but Speedy throws it back. Daffy gets an idea and tells Speedy that he's got a fancy record-manufacturing booth in the lab so Speedy can record his music into it. This booth is actually the time machine. When Speedy tries pulling the chain (to activate what he thinks is the recording activation switch), he breaks it in two. Daffy rushes in to fix it, but Speedy plays his trumpet at Daffy, causing him to accidentally pull the chain and activate the time machine! They go back several hundred years to 65 A.D, and nearly get struck by a speeding horse chariot. Daffy calls him a "fathead", which makes the ancient Roman angry (Daffy tries to lie, but Speedy rats him out) and this sends them to Nero's coliseum. They're thrown in the arena, complete with an angry lion who charges toward them. Daffy uses the wooden sword to slice through the lion's mane, which gives him a crew-cut. This makes the lion angrier, and as Daffy ditches Speedy, he eats the sword. Then he grabs Speedy, who offers him chili peppers. The lion eats them, but then spits fire and trails into the air like a Fourth of July fireworks display. When he comes back down, he chases our heroes up a pole (Daffy conks him with the pole top). When the big cat bends down the pole, Daffy bites his tail, giving them the slingshot treatment. They land on Nero's throne, destroying his violin. Nero starts chasing them, but is too fat to use a chariot. During the chase, they must stop and wait at a traffic signal (complete with a red/green torch). Suddenly, the professor sees this on the time machine monitor and brings them back to 1968. Nero realizes he cannot go back, but Speedy's got an idea. When Daffy goes to bed, he is woken up by Speedy's mariachi band, with a new member, Nero playing his violin!