The bomb is four years old, hence the episode title (very nice of the newspaper that was part of said bomb to save a dated header intact—seriously, Art couldn't make it look a little more realistic?). And for more pseudo-Sherlock Holmes connections, Lisa Edelstein from House M.D. is a guest star on this episode too. The semi-flirt between her and Holmes echoes her role on House as well. Although her very quick answer to Holmes's question about who might want to bomb her company tips her hand early. (As does the flirt for that matter.)
At least we manage to identify and then almost immediately eliminate a number of potential perpetrators; it was a nice change in pattern and pace from more or less every previous episode. But we're still stuck with the fact that the writers continue to try to "spring" the answer on us long after we've figured it out and can no longer be surprised.
More interesting is Holmes's separation anxiety. How it must rankle him to know his condition is "quite common" as Watson points out. Holmes hates to be common. But he can't resist Alfredo's suggestion that he at least attempt to break into a car with a top-rated security system. And like a proud mama, Watson watches her boy go out to play with the other