SOURCE: The Bakra
When we meet Lord John Grey again we realize he wears the sapphire Jamie gave him as "a token of their friendship" which we all knows means that John has it bad for Jamie. Meanwhile, Geillis is looking for the third sapphire which was removed from the treasure box on Selkie Island. She believes that if they all three are brought together with Margaret Campbell's abilities the Brahan Seer's Prophecy will be revealed. Geillis manages to accomplish this goal and we get:
When twice twelve hundred moons have coursed.
'Tween man's attack and woman's curse
And when the issue is cut down
Then will a Scotman wear a crown.
Geillis and Archibald Cameron decide on the meaning of the prophecy: The twice twelve hundred moons refers to 200 years time. The man's attack and woman's curse is the conceiving and birthing of a child. And cutting them down means to kill the child but it would appear it is referring to a 200 year old child.