Um, why did I only get one episode of pink haired Felicity? The audacity. Also, why do Laurel and Dinah have so much screen time? They are my least favorite characters.
Anyway, Felicity is trying to do whatever she can to take down Diaz and is getting frustrated that John is doing everything all ARGUS-like. he keeps saying that while he sympathizes with Felicity, his main objective to to get back the weapon that Diaz managed to steal from ARGUS.
So, Felicity decides to try to hack into anything she can think of, but Curtis stops her, so she settles for following thermal hot spots (or something like that). This leads them to figuring out that the weapon is on a train, but the Longbow Hunters are also on this train.
Felicity is playing Overwatch for John and ARGUS, while they infiltrate the train. They end up setting off some toxic gas and locking them in a train car. When this happens, John sees Diaz out the window, which distracts Felicity and she ends up taking more time than necessary to unlock the door. But, once John is free, he goes after Diaz.
The two of them fight, during which, the weapon falls out of Diaz's pocket. And instead of going after Diaz, John goes after the weapon. Once he gets it, he instructs Felicity to pull the train car off the rest of the train. She hesitates as she knows that this means Diaz gets away, but John convinces her. So, we've got the weapon, but no Diaz. Afterwards, Felicity tells John that she understands why he needs to do things this way, but she can't. So, she ends up going to Watson to ask for help.
Back in jail, Oliver is trying to get information about Diaz. One of his cronies, tells him that he'll give him the 411 if he takes out a specific guard. But, since he didn't tell Oliver how it needs to be done, Oliver sets it up to look like the guard stabbed him, and he gets hauled out of there by some other guards. I don't know why Oliver thinks this guy has better intel on Diaz, than his friends who were literally fighting him today, but I guess when you're in jail, you gotta do what you gotta do.
And Laurel and Dinah are busy being annoying together. That's as much space as I want to devote to the two of them.
Oh, and in the flash forward, we see that William and Roy have dug up Oliver's bow on Lian Yu (and Roy finds something inside the bow that he reads and then sets on fire) and decide to head back to Star City. Why the hell would Oliver and Felicity abandon William? There has got to be more to this story.