NCIS: Sydney wrapped the first half of its freshman season by shedding light on Special Agent Michelle Mackey’s tragic past — yet in doing so left us with at least two burning questions.

In the course of investigating this week’s case, Mackey made no secret of the animus she felt toward a POI — Frank Doherty, a onetime petty officer who, decades ago, had abandoned his post.

Toward episode’s end, when Mackey and J.D. unsuccessfully leaned on Doherty to detail his role (or lack thereof) in the murder at hand, a frustrated J.D. bailed on the interrogation. Mackey, alone now with Doherty, shut off the interrogation room mic, as he asked if she, as a helicopter pilot, had ever killed someone, and looked in their eyes while doing it.

Mackey proceeded to detail how she, while a member of Marine Light Attack Helicopter Squadron 169, was stationed in Khost, Afghanistan, several Christmas Eves ago. When three young soldiers wandered off base and wound up on the wrong side of the border, Mackey disobeyed a direct order to stand down and instead grabbed a gunner and a corp man and took flight in a chopper.

The three soldiers were found and scooped up, but the chopper came under fire on the way back to the border. Heavy with fuels and the extra bodies, Mackey’s bird was none too nimble so she could only bring it in for a hard landing a few miles from base.

“The three guys went home to face the music,” she related. “My two went home in body bags.”

Question No. 1, coming out of this sobering share: Why did Mackey mute the mic, leaving J.D. and Evie oblivious to her tragic past?

“She’s a woman who has built a career on being strong and having an armor, and leading with that strength,” NCIS: Sydney star Olivia Swann told TVLine. “I think that, in her mind, showing any sign of vulnerability to her team would change their view of her. She doesn’t think would be helpful for her role as a leader.

“She’s protecting herself but also protecting her team,” Swann continued, “because when you’re out in the field, when someone knows a weakness it shifts their behavior.”

Also, “No matter how close I think we’ve seen [the merged NCIS/AFP team members] start to become, she’s a very guarded person and, I think, finds it difficult to trust people,” says the English actress.

Yet while we now know what defied order led to Mackey facing a court martial, as DeShawn told Evie in the series premiere, Mackey was eventually found not guilty. Question No. 2 is thus: How could that be?

Swann — who told TVLine “we haven’t even begun to scratch the surface” of what she has been told about Mackey’s backstory — affirmed that the question surrounding the court martial outcome is indeed “very interesting, and I can’t wait for whatever episode it is that that comes out, where we find out the whole story.”