The gang encounter a member (a Constable or Sergeant) of the RCMP (Royal Canadian Mounted Police, "Mounties") in solving the mystery. 1973, the year this was published, was the 100th anniversary Centennial of the creation of the original Royal Northwest Mounted Police. The Mountie is dressed in the well-known Red Serge uniform with Stetson hat and high brown boots with spurs. At that time, the RCMP carried a six-shot .38 caliber Smith & Wesson revolver with a 5" barrel in black steel that was made for them by special order - it had a horse and rider emblem stamped into the metal near the thumb release and is not available for civilian purchase on the used market.
The goose turns out to be an airplane that is disguised as a giant Canada Goose which is used to fly over flocks of grazing geese in order to suck up their feathers by vacuum pressure. Goose feathers are used for warming insulation in jackets and "down" bed covers and are known for their water repellant properties. While they are not especially valuable - certainly not to the extent used in this case, as they are obtained legally by manufacturers through farming - the issue here is that wild Canada Geese are being left featherless and vulnerable and that the method itself is illegal (unlicensed), bringing the attention of the Royal Canadian Mounted Police (though, in fact, the case would be initially investigated by another federal or provincial ministry agent, perhaps involving the RCMP if warranted).