"Grimm" featured Jack the Ripper's copycat killer in episode 20 and fans also watched Juliette continuing down her vendetta-driven path. The penultimate and finale episode of season four promises much action, suspense and an engaging battle as the Royals return.

In episode 21, aptly named "Headache", Nick and Hank continue to investigate Jack the Ripper's copycat killer, reports SpoilersGuide. Their investigation brings them closer to discovering the identity of the serial killer. However, the discovery comes at a cost, as Wu's life is put in grave danger.

Additionally, after turning down Monroe and Rosalee's offer, Juliette continues to plan her vendetta against Adalind by solidifying her new alliance. Lastly, Trubel makes a shocking return to Portland.

Juliette seems to have embraced her Hexenbiestality and has even been enjoying her darker side. Some fans are worried that the veterinarian and witch has gone too far to return to her former self. Is Juliette gone for good?

The promotional clip makes it clear that the problematic serial killer won't be easy to capture. The footage ends with gurgling screams of shock and helplessness, ensuring a nail-biting episode for "Grimm" fans.

The season finale will see the return of the Royals, reports TVGuide. Nick will discover something truly shocking that sets him on a path of revenge against the Royals. Trubel and his mother Kelly will fight alongside Nick to quench his thirst for vengeance. Baby Diana will return to Portland in a slightly different form due to which the Royals will also enter the town with all guns blazing. Viewers should expect at least two deaths, while Captain Monroe will be shot by a friend. TVLine reports that towards the end of the season, Nick will learn that Adalind is carrying his child.

"Grimm" season four episode 21 airs on Friday, May 8, while the finale airs on May 15 at 8 p.m. ET on NBC.