This is a rough demonstration
of an inventory-object puzzle.
Start
You are standing on a porch in front of a door.
A grassy lawn is behind you.
Go inside.
Open the door.
The door is locked.
You will need a key to open it.
Walk over to the lawn.
Go back to the Porch.
You are standing in a grassy lawn.
You see the glint of a key laying in the grass.
Congratulations!
You’ve managed to get inside your own home.
Inventory:
Key?