A Sister's work is never done - not when there are wrongs to right and underdogs to defend. Just returned to their mountaintop hideaway after their latest successful mission, the seven fearless friends enjoy a celebratory dinner and retire to bed. But within an hour, an alarm sounds, and the ladies rush into the compound in time to see Myra and their mentor, Charles, climbing aboard a helicopter. All that's left is a mysterious note, signed by Charles.

Still reeling, the Sisters receive an urgent call from retired justice Pearl Barnes. Pearl runs an underground railroad to help abused and displaced women, and she's just rescued fourteen pregnant teenagers who belong to a highly secretive and controversial polygamy sect. But keeping the girls safe will require the kind of help only the Sisterhood can provide - if they can band together and go it alone.