Calvin asks Hobbes if he's read the papers lately. He says grown-ups really have fouled the world up. Acid rain, toxic waste, holes in the ozone, sewage in the ocean, on and on. They walk a little further, and Calvin says the only bright side is that eventually there may not be a piece of the planet worth fighting for.

Calvin packs his suitcase. He says it's outrageous how grown-ups have polluted the earth. He refuses to inherit a spoiled planet. He's leaving. Hobbes asks him "Where to". Calvin stops, puzzled. He tells Hobbes sometimes he's a real load to have around.

Hobbes suggests they could go to Mars to avoid Earth's pollution. Calvin figures if they go now, they can claim it and keep everyone else off it. Calvin goes off to get their wagon. Hobbes asks if they're going in the wagon. Calvin says of course, unless he wanted to flap his arms. Hobbes scratches his head and says he hadn't thought about that part. Calvin walks off saying "Obviously".

Calvin says goodbye to Mom. He's going to live on Mars, since Earth is too polluted. She tells him goodbye. Calvin stands by the open back door and tells her to say goodbye to Dad. If he can find an interplanetary post office, he'll write once in a while. Mom tells him he's letting in bugs. Either stay in or go outside. Hobbes tells Calvin she didn't see too choked up about them going. Calvin adds they should have left a long time ago.

Calvin and Hobbes are going down the hill in their wagon. Hobbes asks if they'll get enough lift to break the earth's gravity. Calvin tells him yes, he's thought of everything. Hobbes asks what they'll eat on this trip. As the wagon flies off the ramp they built, Calvin tells Hobbes it was his job to pack food. Hobbes says he packed food for him.

Calvin and Hobbes are in the wagon in space. Calvin says they cleared Earth's orbit. Calvin yells "Mars, here we come". Hobbes asks if he's sure this is the way. Calvin asks if he didn't bring the map.

Calvin says space travel makes you realize how small we are. The earth is a tiny blue speck in the infinite reaches of space. Calvin wonders about the mysteries of creation. He thinks they're part of some great design, no more or less important than any other thing in the universe. Everything fits together and has a reason for being. He asks Hobbes if it makes him wonder. Hobbes wonders what happens when you throw up in zero gravity. Calvin tells him maybe he should wonder what it's like to walk home.

They are coming in through Mars' atmosphere. The wagon comes to a landing on the surface. Calvin says they're the first ones to land on another planet. What a historic moment! Calvin tells Hobbes he still can't believe Hobbes forgot the camera. Hobbes crosses his arms and says he did remember the camera. Calvin just didn't want to turn around.

Calvin and Hobbes are walking on Mars looking for signs of life. Calvin notices the old "Viking" spacecraft that landed in the 70's. Hobbes wonders if it's still working. They walk up to the craft, make funny faces at it, and make odd noises. As they walk away laughing, Calvin says that ought to blow some circuits at NASA.

Calvin decides to unpack and set up camp. They have comic books, candy bars, tuna, a can opener, and toothbrushes. They're all set. Hobbes brought along a night light. He thought it might be scary sleeping on a new planet. He goes off looking for an outlet.

As they're eating a candy bar, Calvin comments that Mars is dull, but it's better than Earth. They have the whole planet to themselves. No people, no pollution. Nothing but natural beauty as far as the eye can see. Hobbes asks if that's Calvin's candy wrapper on the ground. Calvin hastily says it was only there a minute, and he wasn't going to leave it.

Calvin and Hobbes both like it on Mars. It's very peaceful. Calvin also adds that Mom isn't there to boss them around. No early bedtime, no baths, no disgusting dinners. Hobbes looks quickly at the ground. He asks Calvin if that rock just moved. They hold onto each other and yell for Mom.

Calvin and Hobbes look at a rock. It's moving. Hobbes says there's something under it. Calvin says it must be a Martian. He says it's probably some creepy, tentacled, bug-eyed monster. They see a tentacle come from under the rock. Calvin says it's coming out. He wonders what they'll do. When they see the Martian, and the Martian sees them, everyone jumps into the air and shrieks.

Calvin and Hobbes are hiding behind a rock. Calvin wonders if the Martian is still out there. Hobbes takes a look. He doesn't see him, so he tells Calvin he must be hiding. Calvin whispers to Hobbes asking if he thinks the Martian is scared of them. Hobbes tells him why not, they're afraid of him. Calvin says they're just ordinary Earthlings, not weirdos from another planet like he is.

Calvin asks why the Martian hid from them. Hobbes supposes Martians may not like Earthlings. Calvin wonders what there is not to like. Calvin yells to the Martian to come out, they're not bad. They just came to Mars because people polluted their own planet. He stops. Then, Calvin asks Hobbes if their reputation preceded them. Hobbes asks if Calvin would welcome in a dog that wasn't house-trained.

Hobbes thinks they should go home to earth. Calvin agrees, thinking they may not be welcome there. He thinks they should fix up their own planet before messing around with other people's planets. As they start down a hill, Calvin says there's only one earth, and it has to last them a while. Hobbes adds they should also go home because they're out of tuna. Calvin hopes Mom and Dad haven't rented out his room.

As they ride in the wagon through space, they approach earth. Calvin says you can see the continents. He says if he remembers his atlas, they live in a big, purple country. Hobbes adds their house is by the giant "E" in the word "States".

Dad comes home from work, and Calvin tells him he and Hobbes went to Mars. Calvin explains they went there because Earth is polluted, but they came home when they found Mars inhabited. Dad asks if he didn't like the Martians. Calvin tells him the Martians didn't like them. He thinks the Martians were worried they'd junk up their planet like they had junked up Earth. Dad asks why his good briefcase is out and why does it smell like tuna. Calvin says they go all the way to Mars, and Hobbes forgets the camera.