Gatekeeper — T.W. Iain

There is a way to enter the Dome. The route is hidden, heavily guarded, and is not for those without inner strength and deep pockets.
Karon is a gatekeeper, watching over the final stretch of this route. Most days, there is nothing to do. Most days, he doesn't see another soul once once he's in the tunnels.
But some days are different. Sometimes, a walker comes to Karon's gate. Sometimes, they pass through into the Dome.
And sometimes they come back.

Gatekeeper is a short story prologue to the dark Dystopian series Dominions.

This short story, complete in itself, is also the prologue to the Dominions series.