You'll start the mission in the Gadget Room, with G on a seismograph. He believes that someone is purposely causing them, and will ask you to go outside and check. At the Dock, you'll see Herbert coming out of the ground in a giant tunneling machine! He has tunneled all below the island, and has made a map of the underground. The map flies away, and Klutzy cuts it in half. Herbert claims to have the directions memorized and heads back into the tunnels. Klutzy drops his lantern, so you can take it. For now, you should report back to G in the Gadget Room.
G will order you to try and follow Herbert down the tunnels. Before you leave and search for the map, you can grab some tools from the Gadget Room. What you want is the propeller hat, the hammer, and the Super Helium, although you have to ask G before you use it. Go to the Sport Shop as well, and pick up the pegs.
Visit the Lighthouse, and you'll see an orange penguin tying balloons. He's done with them, so you can take the whole box. There's a purple penguin surrounded by barrels of Cream Soda that were shaken up by the tremors. You can have a barrel, although it will explode if you shake it up too much. You can make it explode by selecting it in the inventory and quickly moving your mouse around. Before you leave, remember to grab a net from the pile.
At the Town, things are a lot more serious. The Coffee Shop is messy, but the Gift Shop is half underground! You can raise it, though. Just use these items in the following order: balloon inflated with Super Helium, net, pegs, hammer. Be fast, as you have a limited amount of time before the balloon pops and you have to do the sequence again. One half of the map that you were looking for is stuck on the Night Club sign. Enter the Coffee Shop, and tell the barista that you will clean up the cookies he spilled. They'll give you a free cookie. There's a Green Puffle outside the Night Club that you can give the cookie to, and he'll gain a propeller hat and try to reach the map. You can go back to the Coffee Shop and get another cookie. Give him the propeller hat from the Gadget Room first, and then the cookie, and he'll knock the map down from the sign before zooming off. The other half of the map flew towards the Snow Forts!
At the Snow Forts, the map is stuck to a flag. Get it off and it will fly towards towards the Plaza and right into the newspaper of a penguin waiting in line for the Stage. You can't have the newspaper, because he is not done with it yet. Although the penguin would like a double meat pizza with extra grey fish, and he might trade his paper for that. Go to the Pizza Parlor and talk to the Pizza Chef, will give you a double meat pizza with extra grey fish. Trade it to him for the newspaper.
Now that you have the full map, go to the tunnels at the Dock and follow it. The map is randomized each time you do the mission. You can use either Klutzy's lantern or, if you own them, the Dark Vision Goggles to light up the tunnel. At the end of the tunnel, you'll find the Gift Shop if you have not lifted it up yet. If it is still there, unscrew the pipe with the Spy Phone wrench, and use these items in the following order: shaken cream soda barrel, net, pegs, hammer. In the next room, you'll find Herbert's digging machine. In the back, there is the Clock Tower gear from the last mission! Unscrew it with the wrench in your Spy Phone and take the gear. The next tunnel leads to the Boiler Room, where Herbert and Klutzy are attempting to steal the boiler! Approach Herbert and he will hit the boiler out of frustration, causing it to steam. G will call you on the Spy Phone and ask if anything happened. He'll tell you that you should fix the boiler for now. Play the mini game and fix it. Report to G in the HQ, and give him the gear, if you have it. He will congratulate you for your work, and the mission will end.