“Field of Fire” is episode thirteen of season seven of Star Trek: Deep Space Nine.
The episode opens in Quark’s with Julian making a toast to a Lieutenant Hector Ilario, as proof that Starfleet Academy produces the best fighter pilots, as he successfully helmed the Defiant in a battle with several Jem’Hadar warships. Bashir and O’Brien say that if there is anything Ilario wants, he just has to ask. So he asks to join them in the holosuite. Well, ask for anything but that.
Quark tells Miles and Julian that their holosuite is ready, so they depart, leaving Ezri and Kira with Ilario. Much, much later, Ilario is still drinking, even though Kira and Ezri have had enough. Which they tell Ilario, and Ezri escorts him back to his quarters.
The next day, Ezri waits up to a commotion. Ilario is dead in his quarters. Shot with a gun. That fires a bullet. Which is highly unusual, to use a chemically-propelled weapon, not a phaser. The bullet was tritanium, which strikes a chord with Sisko. Starfleet made a prototype projectile weapon, a rifle, the TR116, but abandoned it in favour of a modified phaser. The plans for the rifle still exist, but only Starfleet officers could access the plans to replicate one. Which doesn’t eliminate the suspect pool much.
Ilario was shot at close range, but Odo says that there are no powder burns – he reads 20th century hard-boiled crime novels. Ilario was shot only ten minutes after Ezri left, and she wishes she had stayed behind. And Julian and Miles wish they’d let him come to the holosuite.
Julian asks how someone could do something like that, and Ezri says she knows exactly how such a person thinks, thanks to Joran Dax, the hidden host, and killer, whose existence was revealed in “Equilibrium”. This stirs up thoughts of Joran, who tells Ezri to bring him to the surface to help.
There is another murder, again at close range, even though a rifle is not suited for that sort of work. Which, O’Brien realises, is because the victims weren’t actually shot at close range, which is why there weren’t any powder burns.
There are too many suspects, and the victims seem to have no connection, so Ezri does the ritual of Emergence to bring Joran to the surface, and he does prove helpful. He wants Ezri to think like a killer, and feel like a killer, which also proves to be more than a little disturbing for her. Joran seems to be trying to provoke Ezri into becoming a cold-blooded killer too.