Bob Swanson had hit the ground running. Twenty minutes after his arrival on Phobos, he was already holed up in the old command center. And it was a good thing, too.

His actual mission had only been reconnaissance. The base command men wanted to see if any enemies had survived the initial action. They said that the coast was almost certainly clear, but they wanted to be able to "assure all personnel that no enemy presence remains on Phobos."

They were wrong. Terribly, terribly wrong. But should that be a surprise? Only one Marine survived the last time, after all. It should have been obvious. But here he was, stuck in a decrepit building – a building with a toxic waste storage system full of leaks – and surrounded by alien things from the wrong side of the universe.

He watched the door. Twice - twice in twenty minutes! - he had nearly been ambushed by zombies. When they didn't groan, they moved very quietly. Luckily, they were slow - even if they snuck up on you, they were easy to shoot before they could do anything. They were terrible at aiming, too – worse than he could imagine a real human could be. There was another critter he'd met, though ... Well, in this small room, he could hold out against almost anything – there was only one door, which he could defend forever. But his mission was to explore the whole complex.

With an imprecation at the people who had assigned him here, he moved out cautiously. Damned bureaucrats, he thought, sending a man here with nothing more than a pistol – "suitable for any likely threat" my arse.

He moved carefully, completely alert. There had seemed to be a surprising number of zombies so far. Turning a corner, he muttered, "There you are, deadbrain!" He fired a single shot. "Tarnation!" It was only a grazing hit. The zombie turned on him, revealing the shotgun it carried. Leveling the barrel, it slowly began to aim - then fell backward as Bob's bullet tore into its head.

Bob gingerly picked the shotgun from the fingers of the ill-smelling zombie. He took an alcohol swab from his medical kit and wiped the stock. No one had any idea if zombies carried diseases, but they certainly smelled germy. Seeing that it was fully loaded, he chuckled. Now he was really in the pink. A shotgun! The worst thing he'd seen so far was a brown-scaled thing that looked like a man who had grown spikes on every joint. He had had trouble getting through those scales with just the pistol, but a good military slug gun like this one should take those guys down easily.

He opened the next door, stepping back as it rose. Behind it was one of those brown spiky beasts. "Speak of the devil!" he groaned. The thing was about five and a half feet tall and wasn't as muscular as Bob was, but it had nasty curved claws and a thick beak.

Before he could do anything, the spiky thing exhaled an ugly, grayish vapor and clacked its beak. It must have made a spark, because the creature's breath ignited! A flaming chemical cloud blew towards Bob.

"Damn!" he swore, dodging the fire, though the polluted vapors stung his eyes. He raised his gun; as soon as the tear cleared from his vision, he fired. The shotgun slug blew into the thing's chest. It fell dead, but Bob was a little shaken. They'd said in the briefing that these spiky things could breathe flammable gas, but he never imagined they had that kind of range! Fire! What was next, a biological plasma gun?

Recovering his composure, he walked over to the dead ... alien? Devil? He wasn't sure what it was - the scientists on Mars Base kept assuring everyone they were perfectly natural, if extra-terrestrial, organisms, but most of the other Marines called them demons. This thing was certainly ugly enough to be from Hell. Whatever its origins, it had nothing useful to take, unlike the zombie's gun.

He wondered what would be next. The briefing photos showed zombies, this thing, and a pink carnivore; and there were rumors of other things. At least he hadn't seen any of the Really Bad stuff people talked about. One man said that someone from the Deimos clean-up team saw something like a goat-headed man, only it was an ugly purplish-red like skinless muscle. Ugh! Bob hoped never to see anything like that.

Shrugging, he continued through the corridors of the command center. Duty called...