The gun is given to Twinsen by one of the dissidents, in their hide-out. It is necessary to access the harbor of the Island of the Francos, because it's the only weapon that can reach the levers that open the door in the passage that leads to the harbor.
"You now own a laser-pistol in working condition. It gives you enough firepower to reach distant targets that your magical ball cannot reach."
- The pistol is sometimes refered to as the pisto-laser of Zarnon. It is unknown what/where/who Zarnon is.