The House of Homeless Robots

They always travel in pairs.
It is the only way they can survive.
They must wind each other's clock springs in order to continue their journey.
None powered by batteries have ever made it.
They arrive at all hours of the night -
perambulating methodically, precariously,
each in its unique own way.
Most are made of tin; some are plastic;
a few are hybrids made of composites.
The latter group is considered inferior.
They are all searching for the Key Keeper -
the one who possesses the Universal Key
capable of winding their tiny clockwork mechanisms,
giving them perfect eternal perpetual motion.
They only stop here because it is safe.
The able ones leave in the darkness of the next night -
sometimes with a new partner, sometimes with the same partner -
after going through an almost Darwinian process
of weeding out those no longer fit to continue the journey.
Where the they go is unknown - it is forbidden to follow.
Those that remain behind,
those who no longer have partners
to wind their clock springs, run down and stop.
Their motionless carcasses litter the floor.
Occasionally, one will jerk into motion -
spasm - from the release of some small amount of pent up energy
left in the spring.
Then it is over.