Cotter Oren is a checker-pilot, an elite group tasked to 'meet and greet' travellers from deep space who arrive in the automatic net around the planet Randar.
His job is to locate and remove the arriving ship's 'sealsafe', thus nullifying any possible hostile intent, and sending the passengers and crew to the surface for psychotherapy, which most require after their long journeys.
But during one shift, he is ordered by Flynn Rose, his controller, to check a ship which is supposedly of five thousand kilometers radius - unimaginably large, and therefore considered to be potentially hostile.
He tries to recall the events of his journey into the ship... Oren approaches cautiously in his miniaturised checkership, lands and is able to enter via an airlock.
A still-functioning security system directs him to remove and deposit his checker-suit and weapons (which render the user invulnerable to almost any attack) and he continues on his way to the ship's centre of gravity, where the sealsafe must be located.