In Night Watch, Gerald Leastways, an otherwise rodent-like figure of a man nicknamed "Ferret" by his associates, resides at the YMPA, a circumstance his fellow residents must feel less than secure about. For Gerald is an officer of the Cable Street Particulars, a remarkably nasty secret police notorious for assisting people to disappear in the wee small hours of the morning. If they return to human ken at all, they are somewhat altered by the experience. And generally not for the better. It is believed Gerald enlisted because it gave his small life some greater significance and he believed he would present a better aspect to women - at least, those he did not meet at three in the morning in circumstances where nobody is at their best. To make himself more interesting, he wears a silver Death's Head ring.
He is fascinated, like Nobby Nobbs in a later era, by weapons, even carrying wrist knives - an idiot's weapon, as even the assassins think. Nevertheless, all of his personal weapons carry the engraved initials "G.L." - strictly against orders in an institution where while on operations, members are enjoined not to carry anything that could identify them. John Keel takes advantage of this manifestation of ego to positively identify Gerald when he comes a cropped and ends up in detention himself.
He is also one of the provocateurs, who mixed with the mobs and threw things at coppers and soldiers, and heated the situation up.
Gerald also becomes the first victim of the Ginger Beer Trick, as demonstrated by Keel to the rest of the then Watch. This does not endear him to his mates who have been arrested with him, who later apply rough justice with fists and feet.
In British Army slang, a "ferret" is slang for a soldier trained in basic searching and intelligence/interrogation techniques. Trained "ferrets" were vital in house-searches of suspected terrorist sympathists in Northern Ireland: skilled both in "ferreting out" hiding places for incriminating material and, more subtly, in watching the householder's face for reactions suggesting the search was getting warmer or colder.