An old friend from season 2 needs Sherlock’s help in this week’s Elementary season 3, episode 3, “Just a Regular Irregular.”

Even Sherlock Holmes admits when he is in over his head. To ensure he never fails, Sherlock assembles a legion of experts in every field that he could possibly imagine needing a consultation. You may have noticed Sherlock’s “irregulars” making appearances across the past two seasons of Elementary. While most of the conversations take place with a “contact” on the phone, on some rare occasions a shirtless man will appear in the den working on a math problem.

This week’s Elementary season 3, episode 3, “Just a Regular Irregular,” brings back Harlan Emple (Rich Sommer, Mad Men), as the math genius who last assisted on a case when mathematicians working to solve P versus NP were being murdered. The math world is targeted yet again as a math themed scavenger hunt turns up dead bodies and leads Harlan to seek Holmes’ help.

Synopsis

“Sherlock helps a math genius from his network of “Irregulars” experts after he stumbles upon a body while participating in a math puzzle competition. Meanwhile, Joan attempts to extend an olive branch to Kitty after she learns about the woman’s past.”

Judging by the stills alone, it looks as if Kitty may smack the olive branch right out of Joan’s hand! But knowing how much it means to Sherlock that the two of them figure out a way to work together, we expect some edgy conversations under the mask of politeness.

As Sherlock mentioned to Joan last week, Kitty does not wish to be defined as a victim. Joan now has the added layer of knowing about Kitty’s past to work through as she tries to strike up a working relationship.

Watch Elementary season 3, episode 3, “Just a Regular Irregular,” Thursday, November 13 at 10:00 p.m. ET on CBS.