The CW has released the synopsis for episode #309 of Supergirl, which you can check out below. The installment, titled “Reign,” is officially described as follows:
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REIGN CHALLENGES SUPERGIRL – Supergirl (Melissa Benoist) investigates a mysterious symbol popping up all over National City, tracing its origins back to an ancient prophecy and the mark of the World Killer, Reign (Odetee Annable). Meanwhile, the tension between Lena (Katie McGrath) and Morgan Edge (guest star Adrian Pasdar) continues to build, causing James to step in and offer up some protection, and possibly igniting a spark in the process.
Supergirl, “Reign,” was directed by Glen Winter and written by Paula Yoo & Caitlin Parrish. The episode airs Monday, December 4, at 8pm on The CW.