Let me tell you what was going on around them in my second season finale fantasy (note that it's incomplete and not fully thought through):

Book turns out to be a traitor. He uses his friendship and closeness with Jayne to take him out of play, and Book's friendly demeanor completely drops away, replaced by a cold, uncaring mask. Book calmly returns to his room and puts on a pair of blue gloves.

He disables Zoe, subdues and ties up Kaylee, and then savages Serenity's engines while she pleads with him not to do it. He seals Mal and Wash in the cockpit as the ship begins to lose control and important pieces are starting to break. Book goes to Simon and River. River has lost control because she knows what's happening. Book tells Simon that if he tries to stop him, he will kill him. Then he tells him that the engine room is getting very hot with little Kaylee inside, and soon the engine is going to start exploding, and Kaylee will be destroyed. He then nails Simon in the gut and takes River, and her screams echo through the ship as Book drags her toward a shuttle.

In the cockpit, Mal is coming up with a plan of action. There's only one way out of the bridge, and that's through the front windows -- but there's only one vacuum suit on the bridge. Mal tells Wash that Wash is going to put it on, and that's a gorramn order. They argue, but Mal is adament and scary. He turns to get the suit and Wash takes Mal's gun. He tells him to put the suit on, sir.

Mal, deadly angry, puts the suit on. The ship is beginning to lose orbit around whatever planet they're near. Wash asks Mal to take care of them for him -- Wash is the only one at this point who knows Zoe is pregnant -- and then shoots out a front window. Wash is sucked into the void of space and dies.

Mal gets out of the cockpit but is too late to stop Book from escaping with River. Simon has rescued Kaylee and together they stop the ship from falling apart and killing them all.

End season two. Next: Season Three, The Search For Spock. Er, I mean for River.

I'm sure whatever Joss could have come up with would have been a better way to kill Wash, but those were my idle musings. They'd need refinement to be a real set of tv scenes, of course. I'm not even sure if Mal's weapon could break Serenity's front windows; I imagine those things are pretty tough.

I also know after Serenity that Book wasn't a hands of blue guy. He was an ex-Operative who wanted to leave that life behind.