Emma and Hook might be facing the greatest challenge to their relationship yet when the pirate gets a taste of the darkness and loves it, according to the latest spoilers for episode 10 of "Once Upon a Time" season 5.

In the last episode, Emma's last ditch effort to save Hook by binding him to the Darkness may have backfired.

Jennifer Morrison teased "Once Upon a Time" season 5, episode 10 spoilers to Entertainment Weekly as she said that unlike Emma, Hook will take to Darkness like fish to water.

"As soon as the Darkness is within him again, he goes straight back to his vengeful pirate-y self, pre-Emma Hook, basically," the actress said. "He's operating from the Darkness, instead of the goodness that he's fought for for so many hundreds of years. In the immediacy of it, he's very resentful, but he's operating out of that Darkness that's within him."

The synopsis for episode 10 of "Once Upon a Time" season 5 teases plenty of spoilers as it reads, "In a Camelot flashback, Hook becomes a Dark One and his lust for revenge against Rumplestiltskin is reignited."

"When Emma and Hook disagree about their best course of action, the final pieces of the puzzle are revealed as events in Camelot catch up to the present and we witness a charged confrontation between the forces of light and dark that sends our heroes on a collision course with destiny."

Hook's thirst for revenge against Mr. Gold will put them at a crossroad, one that might not have a return trip.

"Emma's love faces the ultimate test as she tries to convince Hook to turn away from the darkness before she, Mary Margaret, David and Regina embark on a new mission as an unsuspected evil is released," the synopsis added.

Watch out for more "Once Upon a Time" season 5 spoilers which will be published here when they become available. Episode 10 will air on Sunday, Nov. 29, on ABC.