Sherlock (Jonny Lee Miller) and Joan (Lucy Liu) will take on their most difficult case yet in the upcoming episode of the CBS series "Elementary."

In "Down Where the Dead Delight," CarterMatt reports that while the dynamic duo are master sleuths in making sense of evidences to solve a case, this time, they have to make do without a shred of proof. The culprit who blasted the morgue in New York City made sure of that. Holmes and Watson are left with nothing to sift through, which makes the task of finding the killer doubly difficult. If there are no evidences to work on, how will they solve the case? Both detectives will have their work cut out for them on this one, as they find other means to approach the investigation.

Meanwhile, Watson will not know what to make out of a nemesis' request. A New York Police Department (NYPD) detective, someone she has been having "a grudge match" with for quite a while now, is asking her expertise as consultant on a case. With their current relationship, Watson is fully justified for being suspicious. What does the agent want from her? Is he planning an elaborate set up to discredit her work? Watson will have to very careful in accepting the offer, or she may find herself with the short end of the stick.

Last episode, a cold case was reopened when a key witness turned herself in to the police. According to her, she knew who killed the man in his apartment a few weeks before. Before that, the authorities believed that the victim was just one of the casualties of the recent break-ins happening in the city. It turned out, the case had something deeper going on than a simple robbery.

The witness claimed the man was murdered because he was a whistle blower in the shady recruitment practice of a private university. When she also turned up dead, the detective turned their sights on a school president. He had good alibis, though, and Holmes could not pin the two murders on him, especially when a hit man admitted to both crimes. At the end, though, Sherlock was able to prove that the president hired the man, who owed a lot of money from the university, to kill the snitches.

"Elementary" season 4 airs Thursdays at 10 p.m. EST on CBS.