"Come on, Janice! We're almost there!" Maurice hissed as he helped Janice get to her feet and reach running speed again. Moments after the stairway was out of sight she heard the shattering crash of a shotgun, probably through the door given the sound of splintered wood that followed. They hadn't even tried locked the front door in their rush, but their pursuer preferred direct efficiency over subtlety. The ensuing footsteps weren't rushed, but heavy and methodical. If either of them pulled their pistol and tried to ambush at a corner, their foe would be too likely to match the shot with the more favorable weapon of the fight.
Janice scrambled into the master bedroom right after Maurice. No mirror. Maurice opened the door on the far right side of the room. A closet. No mirror on the inside door. In that moment of Maurice's dismay, Janice managed to reach the other side and throw open the door, feeling a burst of jittery relief as it revealed the master bathroom. This was definitely a house that neither of them could ever afford. It was even bigger than the dining room in her parent's house. She fumbled for the light switch so she could see where the mirror was, and the fluorescent glow treated her to the sight of a full-wall mirror opposite of the bathtub and shower. "In here!" She quickly shouted to Maurice. As her partner ran in she noted the absurd scale of the amenities. Surely the bath and shower could each hold a dozen people properly, wasteful unless the owners intended to hold orgies in this house. Realizing she was wasting time as the rhythmic sound of booted footfalls grew ever louder, she turned and threw herself into the mirrored surface.
The other side was, of course, a reflection of the world they were once in, but at the same time even more alien. Light here behaved strangely, giving everything a color palette both darkened and inverted from the original. Janice turned just in time to see the path to the reflected bedroom, and the barrel of the shotgun peer past. Reflexively she grabbed Maurice and pulled them both inside the bathtub. The reflection of their pursuer couldn't see them, but the original could still see them through the mirror if they weren't careful.
Hidden behind the lip of the tub, Janice considered their options. Their noise and image would travel back to the unmirrored world without hindrance, so they had to move with stealth. If they were spotted, the enemy would shoot the place they should have been standing in the real world, then quickly begin to piece together what was actually happening. He'd shoot the mirror, and the shockwave resulting from the shatter would leave them a gory mess before they'd get out of range. It was why this method of hiding was their last resort. Most surfaces reflective enough to do this with were fragile and had easily killed other agents, so they didn't know the full possibility of what could happen.
The pursuer stopped, grunted with frustration and stomped away, their reflection moving towards the tub Janice and Maurice were hiding in and leaning over to look in. This was the other part that kept agents out of the mirrored world. Living things were obviously represented on this side as well, but it didn't work the same way. Features would distort, skin rippled as if it merely housed air, which it possibly did. No one had tried to see what was inside of a person's reflection yet. The effect gave this man the impression of lizardesque frills on his neck in constant oscillation, with the less pronounced ripples adding to the sense of intellect and cold malice on his face. Presumably satisfied that the tub was empty, the original's footsteps moved towards the shower stall, and the duplicate moved in kind.
Janice quietly move her hand to her holster, pulling out her gun. Objects launched from this side would pass through the mirror and land in the real side without problem, given what few tests they had done with the technique. Though it was always rubber bands and paper airplanes and other things that wouldn't shatter the mirror and kill the tester if the mechanics didn't work as expected. Gunfire was untested. Maurice shifted position next to her and looked at the gun, then to her. His expression became severe. Wait it out. He mouthed, not daring to speak the words.
She hesitated. Surely this killer would eventually leave and give them the chance to reenter the real bathroom and escape. This world didn't hold up well enough outside of proper line of sight to a mirror, otherwise they could have already been on their way to pick any mirror within several blocks to exit from and make their escape. As she thought through the rustling of the shower curtain stopped, and the blast of the shotgun rang from both bathrooms, amplifying the deafening noise and shattering plaster. He was checking for hidden wall compartments, and would soon shoot the mirror in order to eliminate that possibility. Ignoring Maurice's urging, she sat upright in the tub leveled a two-handed grip on the killer in the real world, and fired eight shots into his back.
Their pursuer hit the ground as Janice took in the fact that she was still alive. The mirror didn't shatter from this side, allowing her to execute the perfect ambush. As the shotgun stopped clattering on the ground she heard a second, closer thump. She turned to see the reflection of the dead man on his knees, shocked expression staring into the empty space of the damaged shower stall. Maurice was watching him as well, white as a sheet. The dead reflection lifted its hand to stare at, and Janice immediately used the remaining seven shots in her gun, aiming for the head.
Each shot hit its mark, but barely embedded past skin level as patterns like the opaque shattering of bulletproof glass formed around each bullet. The creature, this clearly was no longer person or person-adjacent, didn't even flinch or show signs of impact, and the undamaged portions still rippled as if barely sufficient air pressure was what kept it in its current shape. It turned to look at Janice, alien curiosity on its cracked face. Maurice took his turn next, emptying his gun in a perfect pattern to rupture heart and lungs, should this entity have that equivalent. The results were the same as Janice's attack, but the strange creature wearing the reflected skin of a dead man showed no reaction except mild annoyance.
As Maurice moved his jaw to shout something, the creature grabbed the pearl-white reflected shotgun and swung it stock-first at his head. There wasn't even a shout, just the sickening wheeze of air unable to find a head at the end of his esophagus.
Both Janice and the creature looked at the spatter of off-color gore, her with shock and it with something akin to fascination. Logic began to slowly click back into place for Janice as the creature seemed enraptured by something with in results of its brutality, continuing to hold the shotgun by the barrel as if it couldn't fathom its intended application.
Can't fight it.
Maurice is gone.
Need to escape and destroy the mirror.
Aided by seemingly impossible reserves of adrenaline, Janice sprinted across the bathroom and dove through the mirror, crashing back into a world with normal colors and a corpse that followed the normal rules of mortality. She looked back to see if the monster within the mirror had followed her, but only saw a normal reflection of a damaged bathroom with the unusual addition of more blood spatter than one body could account for. She scrambled to her feet and ran to the dead man, relieved to see that he still followed logic and remained dead in the shower stall.
As she reached for the shotgun by the corpse her world suddenly went white for a flash, then she was staring into her dead pursuer's face. She tried to orient herself, but felt a strangely malleable foot press her head to the floor. The monster's colors were still the darkened inversion of the man it was based on, and it leered over her as she noticed another smaller bloodstain the stock of the shotgun it still held club-like. The expression on it was once again different, not surprised or fascinated, but with a sickening joyous malice.
It raised the shotgun to strike again as darkness took Janice . . .
