In the trailer for "Reign's" next installment, "The Horse and the Hare," Mary (Adelaide Kane) and Catherine (Megan Follows) look to uncover a dark secret of Prince Don Carlos (guest star Mark Ghanime).

With the midseason finale of "Reign" not set to air until the week after Thanksgiving, fans will have to whet their appetite with the latest promo for The CW series.

Last week, Mary sent word to Don Carlos about the possibility of an alliance with Spain. It will be interesting to see how this plays out. With Spain as the greatest power in Europe, there is little doubt Mary and Catherine will look to use this to their advantage.

The episode's synopsis also indicates that Bash (Torrance Coombs) will track down the mysterious killer to Greer's (Celina Sinden) tavern. Also, the new ambassador from the English court, Gideon (Ben Geurens), will make his appearance, raising suspicions of his true intentions.

Of course, Mary will probably continue to recover from her husband King Francis' (Toby Regbo) sudden and shocking death.

While Francis' demise may have been a surprise to some fans, those who have paid attention to history knew it was inevitable. The producers have long maintained that, though they were willing to tweak some events, Francis would not survive the season.

Showrunner Laurie McCarthy spoke with Entertainment Weekly about how this major development would affect the plot moving forward.

"It puts [Mary] in frankly a scrappier position because she's not just losing the love of her life, she's losing the alliance with France and what that foretells is that at some point, she's going to return to Scotland, she's going to lay claim to the throne that is actually her throne in the country that she was born to rule," McCarthy said.

"It's actually going to give her more stories and more challenges," the showrunner added.

The midseason finale of "Reign" will air on Friday, Dec. 4, at 8 p.m. ET on The CW. Watch the trailer below!