Sherlock Holmes (Jonny Lee Miller) seeks out the help of his boarding-school classmate Julius Kent (Owain Yeoman) for a case involving asteroid research in this Sunday’s episode of “Elementary.”

In a sneak peek for Season 5, episode 4, entitled “Henny Penny The Sky Is Falling,” Sherlock and Joan Watson (Lucy Liu) visit Julius at his workplace where the former schoolmates greet each other with an exchange of friendly insults.

“If it weren’t for me, our friend Sherlock would still think that the sun revolves around the Earth,” Julius tells Joan, teasing his frenemy.

“I was eight when I made that mistake,” Sherlock responds in defense.

The British private investigator then hits back by throwing shade at Julius’ solar system-themed vest: “You chose to wear that vest this morning?”

“It was a gift from a fan and how I’m gonna resist?” Julius explains, to which Sherlock replies: “With self respect.”

According to the synopsis for the episode, Sherlock and Joan find themselves drawn into the world of asteroid research while consulting on the investigation of a financial analyst’s murder. Since neither Sherlock nor Joan is adept in astronomy, the two enlist the help of Julius, who is more than willing to explain the scientific aspect of the case in “layman’s terms.” Watch the sneak peek here.

In an interview with TVLine last August, series creator Rob Doherty said that the financial analyst who was murdered in the episode “was looking for better and more efficient ways to identify what are known as Earth-killer asteroids.” Doherty added that that this week’s installment, which marks “Elementary’s” milestone 100th episode, features “a mystery on top of mystery as to why anyone would want to kill someone who might be able to help NASA locate and, hopefully, divert a small planetoid hurdling towards Earth.”

Also in the episode, Captain Gregson (Aidan Quinn) lobbies to include Sherlock and Joan when his unit is chosen to receive a city commendation for its exemplary work.

“Elementary” Season 5, episode 4 airs on Sunday, Oct. 30, at 10 p.m. on CBS.