Even the Transformers are not safe from the Connecticut Yankee Trope...
Warpath and Hoist are battling it out with Starscream, Rumble, Ravage, and Ramjet. When the Decepticons retreat out of exhaustion, Rumble detects energy in a nearby cave. After they wander inside they are transported them to 543 A.D., where they are greeted by Sir Wigend du Blackthorne and his knights, who believe the Transformers are knights of an enemy realm. Their arrival is also observed by an owl, who flies off to inform his master, the wizard Beorht, of this strange new development.
Nearby, Nimue, princess of that enemy kingdom, is spying on their conversation and runs to warn her father, Sir Aetheling the Red, but she bumps into Spike (literally). The Decepticons agree to help Blackthorne's knights win their conflict with Aetheling, but Starscream obviously wants to rule and have a land of his own. Spike enters the jousting tournament between the two kingdoms (which has been rigged by the Decepticons, of course), but quickly fails.
Ramjet and Rumble enter the tournament together (Rumble riding Ramjet in vehicle mode), but are defeated by Warpath and Sir Aetheling. An enraged Starscream is sick of chivalry, kidnaps Nimue and threatens her life unless Sir Aetheling agrees to give up his realm. The Autobots give chase but cannot keep up due to lack of energy and collapse out of exhaustion.
Starscream holds Nimue prisoner in Blackthorne's castle, which he has commandeered, and forces its residents construct and power a primitive electrical generator to keep the Decepticons energized. Starscream then sends Rumble to get potassium nitrate to make gunpowder.
Spike attempts to save Nimue from Blackthorne's keep, only to find she and Sir Blackthorne are now a happy couple. Despite feeling rejected, Spike still agrees to help fight the war against the Decepticons.
Meanwhile, the Autobots and Sir Aetheling's knights charge towards the castle to battle it out with the Decepticons. The Autobots help the knights cross the moat and scale the walls, but they can't put up much of a fight due to their dangerously low energy levels. Starscreams gunpowder projectiles make short work of the invading forces.
Beorht the wizard appears and summons lightning that fills Warpath and Hoist back up to full strength. They take back the battle with Starscream and are victorious. Beorht concludes the robots are time travelers and leads them all back to the cave in which they arrived, only to find it guarded by a dragon. Starscream refuses to go any closer, but Beorht pulls out a pouch of "dragon's bane", noting that a little bit of it works every time. He throws the concoction at the dragon, and it explodes, frightening away the beast.
Spike and the Transformers go back into the cave and return to the present. When they arrive back in their own time, they are greeted by multiple cannon blasts by Megatron. Starscream tackles his leader in a burst of enthusiasm at being back safely. Megatron, on the other hand, isn't nearly as happy to see Starscream, who has just ruined his shot...