There was always reason to fear danger from an Indian attack in hunting on the plains. In 1856, the Pembina hunters were attacked by the Yanktons, near Devils Lake, and their horses, buffalo meat and supplies were taken from them, the Yanktons claiming the parties were hunting in their country without their permission and not for their own food, but for commerce, which they would not tolerate.
In 1860 Sir Francis Sykes spent the summer hunting in the Devils Lake region, and the next summer a wealthy Englishman of the name of Handberry organized a party for the same purpose. He was accompanied by Captain Calvert, Malcolm Roberts, William Nash, and Charles E. Peyton. George W. Northrup was the interpreter and guide. Their entire outfit was destroyed or carried away and the party taken prisoners by the Tetons, but they were released the next day through the friendly offices of the Yanktons, it being represented to them that Mr. Handberry was a British subject and only passing through their country. They were allowed one team by the Indians and escorted beyond the danger line, but the other animals and their outfit and supplies were retained.
From Early history of North Dakota: Essential Outlines of American History By Clement Augustus Lounsberry
Is Handberry the mysterious "wealthy Englishman" mentioned in The Buffalo Hunters of the Pembinah? An intriguing theory, but can it be proven? Doubtful...but just in case, I did pass on the clue and its source to Professor Heather Devine. If anything comes of it, I'll be sure and let you know!