Mourning Cloak is the second of two volumes of Butterfly, but can also be read as a stand-alone novel. Mourning Cloak continues the story of the romance between King Charles I's ward, Lady Mary Villiers, and the King's cousin, Prince Rupert of the Rhine. With the execution of the King in 1649, Mary is forced to retreat to her royalist husband's impoverished estates, while Rupert departs for a long and wandering exile in Europe for the duration of the Interregnum. In such turbulent times, communications inevitably go astray and misunderstandings arise, so that even after the Restoration in 1660 Mary and Rupert remain estranged for many years. The novel concludes with their reconciliation and a final chance of happiness.An intriguing "might have been" of history: if Mary and Rupert had married, as one of his sisters predicted in a letter written in the 1670s, their issue would have inherited the British throne in 1704 instead of Prince George of Hanover, the first monarch of the Georgian dynasty. Both Mary and Rupert had children by other partners, and both were Protestants; Rupert's youngest sister Sophia missed becoming queen by only a matter of weeks.