Queen of France at 16 and widowed at 18, Mary Stuart (Ronan) defies pressure to remarry. Instead, she returns to her native Scotland to reclaim her rightful throne. But Scotland and England fall under the rule of the compelling Elizabeth I (Robbie). Each young Queen beholds her ‘sister’ in fear and fascination. Rivals in power and in love, and female regents in a masculine world, the two must decide how to play the game of marriage versus independence.