Jonny Lee Miller as Sherlock, Jon Michael Hill as Marcus, Lucy Liu as Joan
In a sneak peek from Season 5, episode 20 of “Elementary,” Marcus (Jon Michael Hill) tells Joan (Lucy Liu) why he’s being investigated by NYPD’s Internal Affairs. CBS

A false allegation lands Marcus (Jon Michael Hill) in the middle of an Internal Affairs (IA) investigation in Season 5, episode 20 of “Elementary.”

In a sneak peek from the episode, Marcus tells Joan (Lucy Liu) why he’s being investigated by NYPD’s IA.

“Last night I was driving home when some guy pulled up next to me at a stoplight,” Marcus shares in the video.”He started leaning on his horn, so I rolled down my window. He says that I cut him off a few blocks back, which I didn’t. So I tell him he’s got the wrong car. Light turns green, I drive off.”

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“[But] this morning I got a call from IA,” the police detective continues. “They say, ‘Be here at eight and bring your union rep.’ [As it turned out,] the guy from last night called 911. [He gave] my plate number and said that when I lowered my window I drew my weapon on him.”

Marcus tells Joan that he already told IA his version of the story, but the result of the investigation has yet to be revealed.

“They haven’t decided yet,” Marcus says when Joan asked what happens next. “They could put me on modified assignment until they sort it all out, which is a nice way of saying chained to a desk.” But if things really get worse, Marcus says that the District Attorney could file criminal charges against him.

Joan tries to lift Marcus’ spirit, saying: “That’s not going to happen, people know you.”

But Marcus still has his worries. “People here know me, but to the rest I’m just another opportunity,” he replies.

According to the synopsis for the episode, Watson suspects that the incident that puts Marcus in the middle of the IA investigation is planned by Roy Booker (Robert Christopher Riley), the ex-husband of Marcus’ girlfriend, Chantal (Chasten Harmon), who was first introduced in Season 5, episode 12.

Also in the upcoming episode, Joan and Sherlock (Jonny Lee Miller) investigate the death of a magician who was killed while performing a classic stunt.

“Elementary” Season 5, Episode 20, titled “The Art of Sleights and Deception,” airs on Sunday, April 23 at 10 p.m. EDT on CBS. Watch the sneak peek below: