In 1300, a ship from Lübeck, Germany, docked at Bergen, Norway, and a woman came ashore who claimed she was Margaret and accused several people of treason. Her claim was that she was sold by the wife of Baron Tore Håkonsson, who had been a royal escort on the ship to Scotland, and taken to Germany where she married.
The real Margaret's father, Eric II, had died the year before, and the current king, Erik's brother Haakon V, sent soldiers to arrest them. An investigation ensued.
Her claim was absurd. Eric had insisted on opening the coffin to identify Margaret when the body was returned to Norway. Also, the "False Margaret" was a woman about 40 years old, when the real Margaret would still have been a teenager! Still, people are always ready to believe a good conspiracy theory, and the story of False Margaret and her husband spread quickly. Some of the people willing to believe her may have simply been enemies of King Haakon, looking for a wedge to drive between him and Norwegians.
A year later, False Margaret was burned at the stake for treason; her husband was beheaded. The conspiracy did not die, however. Near the place where she was executed, a small church was built years later called Margaretaskirk ("Margaret's Church"), and a small local martyr cult formed. The church no longer exists, probably demolished during the Reformation.
Meanwhile, back in Scotland...