A natural calamity will rock Scotland in the upcoming episode of "Reign" season 4.

Titled "The Shakedown," tonight's episode will see Mary (Adelaide Kane) take a stand and defend her throne. According to the official synopsis, Scotland gets hit by a tragic earthquake. The Queen of Scots' skills as a leader are tested when she tries to calm her people down after the huge disaster.

John (Jonathan Goad) takes the tragedy as a perfect opportunity to threaten Mary's reign. Charles (Spencer MacPherson) makes a major decision that immediately backfires, while Elizabeth (Rachel Skarsten) resorts to extreme measures after she is seen with Gideon (Ben Geurens).

The sneak peek shows John making sure that he puts Mary in a bad light after the earthquake. "Letting you fall is the best thing I can do for the people of Scotland," John tells the queen, who appears to be infuriated. Darnley (Will Kemp) also becomes a problem for Mary when he begins plotting against her. He believes his wife is depriving him of everything he is entitled to as king, so he comes up with a plan to blackmail Mary.

Elsewhere, Bothwell (Adam Croasdell) discusses Mary's issue with Darnley. The Queen of Scots stresses that she is well aware of the trouble Darnley brings, but she cannot let go of him because he is a "political necessity."

Cartermatt notes that Mary will never abandon her people despite the challenges she is currently facing. However, there are many situations that can hold her back. For Mary, finding a way to aid her people is important not only to cement her image as an honorable leader but also to make sure that she has enough support in case she needs help.

The fourth and final season of "Reign" airs every Friday at 9 p.m. EDT on The CW.