On the 25th of September 1570, it was recorded that the Lady Marion Carruthers "did willfully take her own life by leaping from the lookout tower of Comlongon Castle" where she was being held captive and did "break her head and bones". Subsequently it was noticed that no grass would grow on the spot where she fell and an apparition of a young lady was often seen in and around the castle usually crying.

The events which lead up to her death began when her father, Sir Simon Carruthers, Baron of Mouswald Castle (some four miles away from here), was persuaded to leave his estate to his two daughters Marion and Janet, since he had no son. The powerful Douglas family of Drumlanrig had designs on the estate and Sir James Douglas obtained consent to marry Marion and thus get her part of it. However, another local Baron, Lord Maxwell of nearby Caerlaverock Castle, took and occupied Mouswald Castle, hoping to thwart the Douglas claim. They, however, contested his right to occupy the Castle, stating that they had prior rights by way of a marriage contract.

The case was settled by Privy Council in 1563, when Marion was ordered into the wardenship of Borthwick Castle and told not to try to return home until the marriage was settled. However, she did escape and sought sanctuary in Comlongon Castle, owned by her uncle, Sir William Murray, and shortly after gave over half of her dowry to him, hoping this would persuade James Douglas not to enforce the marriage contract. However, he was not to be dissuaded and instead sued through the courts for his 'just inheritance', i.e. Marion's estate, and he won the case. Marion was ordered to surrender herself to James. Possibly distressed to the point of madness after such a long battle to avoid marriage, she threw herself from the battlements, or so it was said. However, long after her death, rumours began which suggested that some of Douglas's men gained access to her chamber and tossed her from the battlements. Thus, James Douglas was able to obtain her half of the Mouswald Estate without! having to marry her.

Because suicide was suspected at the time, poor Marion was not given a proper Christian burial, and so it is believed that she haunts the castle, forever looking for a proper resting place.