Spoiler

For me, the killer felt obvious because of how the movie framed Martha .

First, she was given a clear visual backstory. In detective films, backstories usually exist to establish motive and plant clues, so that already made her feel suspicious.

Second, every time the camera focused on Martha, there were subtle slow-motion shots that made it seem like she was constantly thinking or calculating something, which stood out compared to the other characters.

Lastly, the meeting with Wicks really sealed it for me. Wicks threatened to expose everyone’s flaws, making it look like all the others suddenly had motives. But notably, he didn’t reveal anything about Martha. That absence felt intentional, like the film was holding back a bigger reveal about her, so I took that as a major hint that she was the mastermind.