The CW has released the official synopsis of Reign episode “A Grain of Deception” (4.02) that will be aired this Friday

A spy threatens Mary’s trust within her inner circle. Queen Mary (Adelaide Kane) discovers there is a leak amongst her advisors and sets out to uncover the traitor. Queen Elizabeth (Rachel Skarsten) enlists in Narcisse (Craig Parker) to further her quest for supremacy. Meanwhile, Catherine (Megan Follows) takes desperate measures to regain some of the power she has lost.