Jonny Lee Miller as Sherlock, Lucy Liu as Joan, Jon Michael Hill as Marcu
Sherlock (Jonny Lee Miller) learns more about Marcus’ (Jon Michael Hill) personal life as the British sleuth investigates Chantal’s assault (Chasten Harmon) and Roy’s (Robert Christopher Riley) murder in  Season 5, episode 21 of “Elementary.” CBS

Sherlock (Jonny Lee Miller) arrives to a sad realization about Marcus’ (Jon Michael Hill) past as the private investigator and his partner, Joan (Lucy Liu), look into an assault involving Marcus’ girlfriend, Chantal (Chasten Harmon), in Season 5, episode 21 of “Elementary.”

At the end of the last episode, Joan found evidence that the man who made a complaint against Marcus was a neighbor of Chantal’s ex-husband, Roy (Robert Christopher Riley). When the neighbor was interviewed, he admitted that Roy was the one who asked him to make false allegations about Marcus. Shortly after, Roy was arrested but subsequently released pending trial. Marcus went to Chantal’s apartment to tell her the good news, but he found her lying on the floor with drops of blood around her.

READ: Rob Doherty talks “Elementary” Season 5 finale, Season 6 renewal odds

The synopsis for the episode 21 reveals that Chantal is alive but is assaulted by someone who broke into her place. Marcus suspects that Roy is behind the assault, and as seen in the trailer for the episode, the police detective tries to avenge Chantal by coming at Roy by himself.

Roy is brought in for questioning, but he insists that he wasn’t the one who hurt Chantal. Shockingly, before Sherlock and Joan can solve Chantal’s case, Roy is killed in a staged suicide. The partners then find themselves looking for one suspect behind the two cases, and the British sleuth discover something about Marcus’ past that might have something to do with the crimes.

In a recent interview with TVLine, executive producer Rob Doherty said that the episode offers “a much better sense of [Marcus’] upbringing and why [viewers] don’t hear much about [his] dad.”

Do you think Marcus’ dad was behind Chantal’s assault and Roy’s murder? Sound off in the comments section below!

“Elementary” Season 5, episode 21, titled “Fly Into a Rage, Make a Bad Landing,” airs on Sunday, April 30 at 10 p.m. EDT on CBS. Watch the trailer below: