Before you ask--no, I have not seen your cat.  
Your cat left the house around 4:45 pm, while you were at work, I'm assuming. I'm assuming your room-mate left the door open and the cat saw an open space, a new world, waiting to be scratched and pawed and possibly snacked on. The cat walked out on you in this way.

The cat padded along the wooden steps, peacefully, quietly.
No one was around except a grasshopper, who died in the cat's mouth later.
Meanwhile, your room-mate brushed her teeth and did mouth rinse for as long as thirty-five seconds.

There were puddles in the road, and a car drove by and water splashed up into your cat's little face.  The little face of your cat winced, and the little body shook off the water, and kept cat walking to nowhere in particular.  Your cat--the zen master.

Seemingly out of no where, a large tree appeared, and the cat walked around the tree to the other side.  A squirrel paused to observe the cat, cautiously.  

Like the squirrel, the cat then proceeded cautiously around his or her own predator, the dog.  The dog was chained to a fence though, and your cat was free.

When you came home from work, you were so tired you fell asleep and did not even notice that your cat was gone.