Elementary Season 1 Disc 6

Episode 21: A Landmark Story
The first time we met a surrogate of Moriarty, not the man himself, presuming he is a man and that she is not a woman. But, of course we don't know this right away, we believe that this particular killer is a serial killer, not an assassin. In fact we don't even know there is a Moriarty until the end, we only know there is a killer who uses the moniker M. Of course the educated audience is expecting the M to stand for Moararty, but it doesn't.
Moriarty is back. Kind of. A man dies of a suspected heart attack and a whole chain of events lead to uncovering other assassins used by Moriarty, each very different from the last. One of these men was an engineer and specializes in killing people in a way that makes it look like an accident.
There is no secondary story going on this time and we get to see Holmes and Watson work on their issues in only one light. It was actually a nice change of pace and done quite well.

Episode 22: Risk Management
This is really the second part of the last episode, as it begins immediately after the conclusion of the last one, which ends with Moriarty calling Holmes. This episode begins with the twist of the phone call continuing and Moriarty asking to hire Holmes to find a killer.
Captain Gregson tries to get Watson to leave because it is too dangerous and at a later point, Holmes tries to misdirect her for her own protection. She will have none of it, rightly stating that if she is not into being a detective all the way, including possible personal danger that she is only playing at it and that they are behaving overly defensively because she is a woman.
Throughout the whole episode, Holmes is at least least one step behind Moriarty and they both know it. As you can imagine this is quite a blow to Holmes ego, but for the most part he puts it aside because the game they are playing is getting him closer to his goal of finding Moriarty to avenge Irene, Holmes murdered girlfriend. Of course, the end of the episode is a game changer.

Episode 23: The Woman/Heroine
Finally we got to the big season closer, a double length episode none-the-less. As you might have guessed from the descriptions of the previous two episodes, this is all about Holmes versus Morirarty. Every single time the two go tet-a-tet, Moriarty wins. That does not change in this episode as Morirarty forces a well known Greek Nationalist with a shady past to commit a crime to save his daughter, and the crime causes a fluctuation in the currency market of Macedonia so that Moriarty makes nearly a billion dollars. Meanwhile, Homes knows what is going on but is powerless to stop it as he is always one step behind.
Holmes is able to figure out Moriarty's involvement and to find evidence proving what he is saying, but it is still too late each time to prevent the loss of life. Not that catching murderers is a bad thing, mind you, it's just that Holmes feels that he should have been able to prevent them.
I don't think I spoil anything by saying that Moriarty lets Holmes that he has been bested and that in every possible meeting of the two that Moriarty will always defeat Holmes, which Holmes knows to be true. But by your powers of deduction, you should already see what I'm saying with this and know what happens in the episode. I won't belittle your mental capabilities by stating the obvious.