After dealing with the dangers of the Underworld, the heroes of Storybrooke will embark on another adventure involving a mental institution in the next episodes of "Once Upon a Time" season 5.

According to the latest casting news about the series, the heroes will encounter a meek but tormented mental hospital patient named Nathaniel, portrayed by "The Man in the High Castle" actor Hank Harris. They will also face Nathaniel's ruthless and domineering warden named Jacob, portrayed by "Being Human" star Sam Witwer.

TVLine first reported the casting for the recurring roles of two brothers who will be introduced in the latter part of season 5 and will return for season 6.

According the report, published March 2, the roles include an evil, morally corrupt character who will do everything to become powerful, even if it destroys his own family. The other character is the younger brother who is a lot weaker and yearns to get out of his ruthless brother's shadow. The roles perfectly fit the description of Harris and Witwer's characters in the series.

Aside from the introduction of Harris and Witwer's characters in the series before "Once Upon a Time" season 5 concludes, Amy Manson also revealed that her character Merida will also return to Storybrooke in the upcoming season finale.

Speaking to D23.com, Manson shed light on Merida's fate in the series after her last appearance in November. "Funny enough, I just found out today that Merida will return for the season finale," the actress shared, via Melty. She also mentioned that she had no idea why Merida will return for the season 5 finale.

"Maybe it will be about planting the seeds for next season. You're the first person to know! I start shooting in early March," the actress added.

The next episode of "Once Upon a Time" season 5 airs March 20 on ABC.