Sherlock comes home to the brownstone to find Marcus just leaving and Joan hopping in the shower.
He immediately jumps to conclusions and believes that theyre having a sexual relationship.
Thats not the only bit of misdirection, though.
Credit: CBS
It seems to be cut-and-dry evidence, but Sherlock notices something strange about the womans inflection.
Things get complicated when the autopsy comes back.
The victim, Ellen Jacobs, was eight weeks pregnant at the time of her murder.
Thus, Sherlock and Joan head over to Ellens house to question her husband, Ernie.
He seems legitimately surprised to hear that his wife was pregnant, but theres more to it than that.
Therefore, Ernie couldnt possibly be the father.
Ellen must have been having an affair, but Ernie swears he doesnt know about any other man.
A visit to Ellens OB-GYN doesnt turn up much evidence either.
The doctor refuses to give up any information about the possible paternity of Ellens baby.
Still, that doesnt stop Joan from searching the doctors computer when shes not in her office.
Meanwhile, Sherlock uncovers the real reason why Marcus was visiting with Joan.
Shes been helping him study for the sergeants exam.
Sherlock is surprised because he thinks Marcus is an invaluable detective.
NEXT: Spare keys and bounties
With that revelation comes another: Harris Grear also had a son.
They saw him with her at La Porte Blanche one day but didnt get a good look at him.
The selfie-takers are dangling keys while they take their picture, and that reveals a connecting thread.
Could he be the father/secret lover?
As it turns out, yes.
He had slept with Ellen a few times but swears he didnt know about the pregnancy.
If thats true, he didnt have much motivation to kill her.
Just when it seems like theyve found their man, Warren is attacked and nearly beaten to death.
After more questioning, he says that Ellen knew who he was and understood his motivation.
Hence, he was the one who was going to visit her father at the prison.
He wanted to confront the man who caused his family so much pain.
Scaffolding surrounds their house, and Marcus finds blood on a specific piece.
As it turns out, hes telling the truth.
Its the same bag from the place where Nolan gets his fish.
With the evidence piled against him, all the detectives want is a motive.
Admittedly, the explanation is a little underwhelming.
When he found out Ellen was pregnant, he killed her.
Not the most exciting ending to an otherwise compelling case.
However, the episode ends on an emotional high note.
Of course, this is Sherlock and Joan, so not everything is as it seems.
Sherlock and Joan wanted to show him how indispensable he is as a detective.
