WOW! I can't believe this is the first Ben 10 and Martin Mystery crossover! Seriously, why hasn't anyone else thought of this?

I might put couples in it, tell me who you want.

Ben 10 Alien Force, by the way.

I don't own anything.

"Are we there yet?"

"Shut up, or we'll never get there!"

"Quiet down you two, we're almost there." Gwen said calmly. She turned the radio in the car on, choosing a rock station. "Let's just listen to music until we get there."

"Fine," they said in unison, Ben dragging it out from annoyance, while Kevin said it angrily. Gwen sighed. Why couldn't they get along for once? They were on a very simple mission: find the ship of an alien that crashed-landed recently. Decide if it was a threat or not. If it was, take it into custody, if not either send it back home or teach it to live peacefully among humans. Very simple, if they could stop arguing.

"Right here," she said, looking at the holographic map from her Plumbers badge, "Pull over."

Kevin did, parking on the side of the road in some bushes. "Come on, we're there." He said to Ben.

"Finally!" Ben jumped out of the car and activated the Omnitrix and transformed (that's what it would be, right?) into Jetray.

""Ben, wait!" Gwen yelled as he flew off. She and Kevin ran after him. "Slow down!" Eventually, they come to a clearing in the forest. Ben, human Ben, was standing in the middle of it looking around confused.

"There's nothing here." He said.

"That's impossible. It says-" Gwen gasped looking at the map. The red dot on the screen was gone. "What?"

"Did someone already take care of it?" Kevin asked.

"I don't know. Maybe."

"But who?" Ben asked. "And why would they bother? We're the closest."

They pondered this in the clearing for a while longer. Coming up with nothing, they decided to leave.

+++++The Center+++++

"That was great!" Martin said as he watched Center officials carry the alien intruder off. "So, Diana, do you believe in aliens now?"

Diana sighed. "Yes, Martin." She said just to please him.

Martin and his step-sister, Diana, had completely different personalities. She didn't want to admit that there was life outside their happy little planet, but that was all that Martin thought about. It confused Martin that Diana could still refuse to believe in life other than humans on earth when she worked for a secret organization that tried to stop alien invaders. Among other (paranormal) stuff as well.

"Guys," Billy said floating into the room, "There is more alien activity in Bellwood."

"You are to go there immediately." M.O.M said, opening a portal.

Diana groaned. "Really? Already?"

"The safety of your home planet comes first, Diana." M.O.M scolded. Diana looked down at her feet, embarrassed, and mumbled an apology. "Now, hurry, before too many people get hurt. Java, you stay to help us here, Billy will go instead."

Martin and Diana went to the portal, Martin pulling a very panicky Billy with him. "Wh-what? F-f-field work? B-b-but-" He was cut off as Martin dragged him through the portal. Diana followed after a quick goodbye.

Once through, there was chaos. There were four people standing a few feet away- no, not people, only one of them looked human. And even she was throwing pink orbs at a… thing, Diana had no clue what to call it… that had tentacles on its face. There was also a teenage boy, she guessed, that was dark grey all over and also fighting the tentacle monster. The final figure was this dinosaur-looking thing that seemed to be able to change its size.

"Whoa," Martin breathed. Raising his voice to a yell, he said, "THIS. IS. SOOOOO. COOL!" All the figures turned towards them as Diana slapped her hand on her forehead.

She hit Martin on the head. "Don't draw attention to ourselves, dummy!" She said. "It could get us in trouble!"

And it did. The tentacle beast lunged at them, only to be stopped by the dinosaur. "Oh, no you don't!" He said, throwing the monster against a building.

The girl came over to them. "Are you ok?" She asked.

"No!" Billy said, only to be silenced by Martin. "Yes! This is the first real action I've had in forever!" He activated his U-Watch. Choosing the I-Cutter, he ran into the middle of the action. The girl watched in wonder.

"Who's he?" She asked.

"Only my annoying step-brother." Diana replied.

"D-d-d-Diana? Th-th-th-the portal's closing. L-let's go back while we have a-a chance." Billy asked nervously. He turned and screamed. "N-n-no! The- the- the portal closed!"

"Diana? I'm Gwen. That's Kevin and Ben is the dinosaur. You want to fight Vilgax." Gwen handed Diana a laser gun. "Hope you can use this." She ran towards Ben, firing pink orbs at Vilgax.

Diana looked down at the gun in her hands. She, too ran to help Martin and the others.