While enjoying the verdant scenery of Scotland in a drive in the Gadget Van, Penny, Brain, and Inspector Gadget are suddenly attacked by a huge dragon-like beast which spits fire at the car. Thinking his engine has simply overheated, Gadget stops the car and gets his latest assignment from Quimby: It's off to Loch Ness to protect an important scientist from the clutches of Dr. Claw. Despite a MAD detour that sends the Gadgetmobile flying off a cliff, and without the help of shocked-to-silence Scottish locals, Gadget finds his way to the Loch only to realize the scientist is already missing. The police inspector begins his search for him while Penny secretly does some investigating of her own. Using a portable computer / radar screen, she tracks not only the monster that tried to destroy them earlier (which turns out to be an enormous mechanical creature), but also the Gadgetmobile and Brain, one after the other, all underwater. The monster swallows Gadget whole, and once inside, he finally meets Professor Thumphkin, a nervous old man in a wool sweater with a voice reminiscent of actor Richard Haydn. In an attempt to break out of their unlikely prison, Gadget uses his laser and his screwdriver, yet succeeds only in freaking out Thumphkin and short circuiting the lake monster's guidance system. Dr. Claw is no longer able to control it from his MAD sub, and it's all he can do to get out of its way. Penny deftly leaps onto the huge robot, literally gets inside its head, and brings it to a quiet stop at the shore of the lake. Gadget emerges from the monster intact, carrying a passed-out, but safe Professor Thumphkin.