 Mary and Percy began meeting each other secretly at Mary Wollstonecraft 's grave in St Pancras Churchyard , and they fell in love — she was nearly 17 , he nearly 22 . To Mary 's dismay , her father disapproved , and tried to thwart the relationship and salvage the " spotless fame " of his daughter . At about the same time , Mary 's father learned of Shelley 's inability to pay off the father 's debts . Mary , who later wrote of " my excessive and romantic attachment to my father " , was confused . She saw Percy Shelley as an embodiment of her parents ' liberal and reformist ideas of the 1790s , particularly Godwin 's view that marriage was a repressive monopoly , which he had argued in his 1793 edition of Political Justice but since retracted . On 28 July 1814 , the couple eloped and secretly left for France , taking Mary 's stepsister , Claire Clairmont , with them , but leaving Percy 's pregnant wife behind . 
