A revealing interview from The Walking Dead star Thora Birch confirms the true allegiance of Whisperer Gamma, who appeared to betray Aaron (Ross Marquand) in the Season 10 midseason finale, “The World Before.” Alpha (Samantha Morton) encouraged Gamma to “wear a new mask” and buddy up to Aaron for information, but a discovery that Alpha lied about killing daughter Lydia (Cassady McClincy) destabilized Gamma's faith in the Whisperer leader. When Aaron, Daryl (Norman Reedus), Carol (Melissa McBride) and a team from Hilltop set out to locate Alpha's walker horde using intelligence provided by Gamma, they found only an empty field before falling into a trap sprung by Alpha — bringing Gamma's true loyalty into question.
Gamma unmasked herself as Mary before giving Aaron information about the horde in exchange for a meeting with her last-surviving family member, nephew Adam. During an encounter at Hilltop, Mary's sister Frances (Juliet Brett) was forced by Alpha to abandon her child, who was later adopted by elder couple Tammy Rose (Brett Butler) and Earl Sutton (John Finn).
According to Birch, Aaron is right to believe he wasn't betrayed by Mary: she “desperately” wants to see her nephew.
“I also think she feels a slight responsibility to Alexandria at that point, and wants to give them the best shot of getting the situation under control, if they can,” Birch says in a behind-the-scenes video published by AMC. Adds Marquand, “Aaron trusts Gamma about the location of the horde because she’s risked a lot to meet him on a regular basis.”
Mary was “surprised by Aaron’s gentle nature with her,” Birch says, and Aaron — a recruiter for the Alexandria community — rightly zeroed in on Mary’s humanity despite Alpha's best efforts to snuff it out.
“I think the desire to engage with Gamma is twofold. One, I think Aaron has the ability to seek out good people in the world, and he does see the goodness in Gamma. He kind of can sense it,” Marquand adds. “And she seems like a very reluctant participant in Alpha’s tribe. The other part of it is that Aaron really wants to get information from her.”
As hinted by the trailer for the second half of the season, Mary could help rescue the stranded scout team from the cave where they're now surrounded by thousands of walkers: an unmasked Mary is seen approaching Alexandria and alerting Father Gabriel (Seth Gilliam) and Rosita (Christian Serratos) about the situation now threatening the lives of Connie (Lauren Ridloff), Kelly (Angel Theory), Jerry (Cooper Andrews) and Magna (Nadia Hilker).