An old adversary reappears in Elementary season 4, episode 11 and this time Joan Watson is not letting Detective Cortes gain the upper hand.

Detective Gina Cortes (guest star Monique Gabriela Curnen) does not appreciate “amateur” detectives poking around NYPD business. Joan Watson does not enjoy being called an “amateur” detective. The last time the two detectives met, Watson and Cortes settled their differences in the boxing ring. Cortes may still have a lingering grudge against Watson when she reappears in Elementary season 4, episode 11, “Down Where the Dead Delight.”

When Detective Cortes comes calling for Joan at the precinct, both Joan and Sherlock instinctively put their guard up. Before meeting up with Cortes, Watson decides to fit in a bit of precautionary training with a little help from Bob.

You go, Joan!

Would Cortes purposefully call Joan for the sake of a rematch? Or does she genuinely need Watson’s help on a case? Cortes likes to play dirty and waving an interesting case in front of a detective is the perfect way to lead them into a trap.

After seeing Joan’s “badge of honor” following their last encounter, we don’t blame her for wanting to be prepared for anything.

Meanwhile, Sherlock and Joan must tackle a case for the 11th Precinct that rattles the dead. The New York City morgue and, by extension, M. E. Hawes are the targets of a bombing that destroyed all physical evidence upon detonation. There’s only one surefire way to get a bomb into a morgue unnoticed — slip it inside a corpse.

This is not the duos’ first rodeo dealing with physical evidence missing from the morgue, but it is certainly going to take Sherlock to some very interesting places. Namely trudging through a marsh.

Watch Elementary season 4, episode 11, “Down Where the Dead Delight,” Thursday, February 4 at 10:00 p.m. ET on CBS.