Saoirse Ronan, Margot Robbie clash in 'Mary Queen of Scots' trailer

July 13 (UPI) -- Saoirse Ronan and Margot Robbie play 16th-century royals who first try to work together, then clash in a struggle for power in the trailer for the upcoming period epic, Mary Queen of Scots.

Ronan plays Mary Stuart, who was crowned queen of France at 16 and widowed at 18. The film follows her as she returns to her native Scotland to reclaim her throne, but finds Scotland and England under the rule of her cousin Elizabeth I, played by Robbie.

"Each young queen beholds her 'sister' in fear and fascination," a synopsis said. "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. Determined to rule as much more than a figurehead, Mary asserts her claim to the English throne, threatening Elizabeth's sovereignty. Betrayal, rebellion, and conspiracies within each court imperil both thrones -- and change the course of history."

Directed by Josie Rourke, the movie is to open in U.S. theaters on Dec. 7. It co-stars Jack Lowden, David Tennant, Brendan Coyle and Guy Pearce.

Ronan, 24, and Robbie, 28, were Oscar nominees earlier this year for their performances in Lady Bird and I, Tonya respectively.

Robbie was recently hired to play murdered actress Sharon Tate in Quentin Tarantino's Once Upon a Time in Hollywood.