Your heart is racing just a bit at the surreal scene before you.
You rush forward to slam the door.
Whether it's the loose, cracked concrete basement floor or that your eyes are still surprised by the ingress of bright, outdoor light into the otherwise dim room, you stumble and fall forward. You try to catch yourself on the door frame but fall through anyway. You bang your shoulder pretty good but the soft turf and tall grasses on the other side break your fall.
You sprawl on all fours and stop yourself from going face-first into the strange, other world.
The sound of birds chirping and insects buzzing remains normal.
Blinking in the bright light of day, you slowly get up and look around.
Sure enough, right behind you, the door frame stands, propped up and planted in the ground at its base like some strange tree. Through it, you can see the dim, dusty basement of the mansion. But that sight isn't what gets your attention.
Behind it, low on the horizon is the moon.
Actually, it's two moons: one bigger than any you've ever seen in the daytime, before, and another, overlapping it, somewhat smaller.
You're definitely not in Kansas any more.
Walking forward, you examine the door again. From the other side, it still looks closed. From the open end, though, it's ... normal.
You step back through and check it out. You can get back and forth.
An itch on the back of your neck, bothers you but you can't be bothered to do anything more than scratch at it. This is an amazing discovery! You retrieve the bronze key from the lock and put it in your pants pocket. You're still looking around, going back and forth through the door to test it, when you realize that -over the last ten minutes since falling through the portal, the itch has been spreading.
You feel it along the sides of your face, now, and down across your shoulders.
Looking, you gape.
Soft, tawny fur is growing over your body.
"What the hell?"
No one is there to hear you but you say it out loud anyway.
You feel a sudden falling sensation in the pit of your stomach and double-over. You lean against the inside of the door frame, grasping it with one hand, as the fur takes on a flash of red and orange, moving swiftly down your arms. You can feel it also covering your chest and back.
You gasp as your bones seem to being molding and shaping like thick, heavy clay under some unseen potter's hands. You feel a pain pushing at the base of your spine and your jaw explodes in a throbbing ache. The world starts to spin and you find your feet hurting as your shoes seem to contract.
Scents and sounds explode in your mind as the world's intensity seems to have been cranked to "eleven".
The dust of the basement... The loam of the fresh earth... The sound of insect wings... The crashing of distant waves... The aroma of a recent thunderstorm...
All of smashes into your senses, leaving you reeling.
Your arms grow more defined beneath the now complete coat of fur and your hands develop black pads on each fingertip. You feel your ankle rise and your feet spreading out within your shoes, getting wider and fuller. A tail pushes out from the waistband of your pants and you feel your cock shifting inside your pants.
A dark shadow pushes out from beneath your field of vision and, shortly, you realize you've grown a muzzle... A slender, canine-like muzzle...
Your world spins as you get dizzy. You manage to hold yourself standing within the door frame -between one world and the next- as your brain tries to come to grips with what's happening to you.
The sounds and smells intensify as the color of the fur on your hands darkens, becoming like black gloves. Whiskers sprout from the sides of your muzzle while the sensations finally begin to ebb.
When they stop, you turn around and around, looking at yourself.
A long, bushy tail flops from behind you as you -painfully- try to keep on your feet. You shuck off your shoes, revealing large, sock-stretching paws and animal-shaped lower legs.
You discover that, in your frantic examination of your body, you stepped through the door once more and -again- are standing in the tall grasses. Through the door, in the basement, you see your reflection in an old, dusty, full-length mirror.
You've become a humanoid animal cross-breed. You stand on two, digitigrade legs but have the distinct characteristics of a ... a fox!