Mary (Adelaide Kane) prepares to take over the English throne on the next episode of "Reign" season 4.

In the trailer for the episode called "Dead of Night," Darnley (Will Kemp) is seen urging Mary to start the war against the English queen, Elizabeth (Rachel Skarsten) before she can announce her engagement. But Mary appears to be reluctant about her husband's plans. This will cause another disagreement between the couple.

Meanwhile, Gideon (Ben Geurens) is seen warning Elizabeth that there will be a lot of Catholics who would support Mary's quest for her throne as long as the Scottish queen is alive. This means that Elizabeth should also attack her if she wants to secure her seat in England.

The synopsis of the upcoming episode also reveals that Elizabeth will continue searching for a suitable Catholic man to become her husband. However, the English queen remains conflicted about her feelings for Gideon.

Meanwhile, the French Court will also have a problem of its own on the next episode of "Reign" season 4. According to the synopsis, King Charles' (Spencer MacPherson) younger brother Henry (guest star Nick Slater) will try to take over the throne with the help of Spain, as well as Lord Narcisse (Craig Parker).

In the previous episode, Charles finally embraced his fate as the new King of France after the death of his older brother Francis (Toby Regbo). It took a while before he seriously accepted the throne because of his party boy nature. Yet, as soon as he decided to accept the throne, his youngest brother suddenly arrived to claim it. But can their mother Catherine (Megan Follows) manage to stop her youngest son from ousting the French king?

The CW is scheduled to air the next episode of "Reign" season 4 on Friday, May 5, at 9 p.m. EDT.