Wait, sexually-based offenses are considered what, now?
We join some kind of case review in Philadelphia, already in progress. Chester's one of the many detectives (both amateur and professional, we'll learn) who are packing the room, and before we can figure out what's going on, he's out in the hallway talking to a woman named Penelope Fielding about another old case. It's the most exposition ever -- all we get is that she knows about a witness that Chester doesn't.
Casey's at some kind of lawyer fete, getting wooed to criminal defense by some corporate type. She skates out when she gets a page. We already know she's going to regret not taking the job.
Cut to a busy late night crime scene, where Olivia, Elliot, Fin, and Munch arrive at roughly the same time. Cragen gives them the bullet: One cop dead, another wounded. The dead one is a Detective Edward Kralik. The live one, and the prime suspect in Kralik's shooting, who they're not even allowed to question? That would be the guy getting loaded onto an ambulance, one Detective Chester Lake. This could get awkward.
Next morning, M.E. Warner wants to take Kralik's body off the scene, satisfied that those five gunshot wounds have done their work. Olivia and Elliot put her off, saying there's a lot of red tape on this one. Elliot further demonstrates his bad mood by yelling at an inspector for standing in a blood puddle. A CSI type shows off a fancy device up on a tripod that's scanning the whole scene into a computer in 3D. But since it can't tell them who shot first (like Chester can), Elliot and Olivia decide to go "check on [Chester's] condition." And if Elliot accidentally gets a finger stuck in one of Chester's bullet wounds, well, these things happen.
In Chester's hospital room, a lucid and stable Chester refuses to answer Elliot's questions about what happened, invoking some police code that prohibits questioning by a superior officer. Which should give Chester protection from just about everyone. After Elliot warns Chester to tell his story so he can protect himself, he and Olivia go back to the squad room empty-handed. Cragen tells them to look into Chester's history with Kralik. Just then, Fin and Munch show up to report that they've discovered that Chester's been making monthly trips to Philly and no one knows why. Elliot bitches at Fin for his ignorance of his partner's movements, but Munch says they'll figure it out. Always the peacemaker, that Munch.