Jack Rowand/ABC
Natalie Abrams
March 13, 2015 AT 08:27 PM EDT

When Regina (Lana Parrilla) goes undercover to infiltrate the Queens of Darkness on Sunday’s episode of Once Upon a Time, a surprising ally will try to convince her against it: Emma (Jennifer Morrison).

Fortunately, by that time, Regina has already learned that Maleficent (Kristen Bauer van Straten) & Co. are after the Author, and are planning to use Regina to steal a piece of information that could help them locate him. How will Emma react? Find out in our exclusive sneak peek.

Once Upon a Time airs Sundays at 8 p.m. ET on ABC.

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