The third episode of Dept. Q ended with Rose possibly finding a connection between the mystery man wearing a hat that appeared to Merritt and William at their home and on the ferry, and their father's boat which is named after the Boobrie bird that's on the cap. Now Dept. Q episode 4 picks up from that moment, and introduces us to another player in Merritt's past. Here's a recap of the episode on Netflix. Spoilers below.
The episode starts with us going back to the moment when Merritt was kidnapped and first put in the hyperbaric chamber. And as Carl and Akram assumed, William's hat had flown back into the parking lot which made the perfect spot to take her without anyone noticing.
After some more digging and Rose visiting the constable in Mhor this time, the team learns that Merritt had gone back home just once after moving away with William the day of Henry Jennings' funeral. Aka the man who beat William up and caused his aphasia. She went back for a necklace that was her mother's, and the constable had circled it for some reason the day of the crime.

More questions arise for the Dept. Q
With Merritt's items also sent over from the Crown Office where she worked, Carl and the team also find a card from a flower store indicating she was meeting someone at a hotel room. It's simply signed "S," which presents another mystery. Who is this person, which hotel did they stay at, and could they be connected to Merritt's disappearance?
It turns out she and her partner in the Graham Finch case we saw in the first episode, Liam, had a brief affair that lasted about a month. Though he's not a suspect right now, the series continues to show us how complicated her life was in and outside of work. They are able to get the hotel information out of him though, and records show that she was checking in as Lila Graham - her mother's maiden name. Ok, Merritt.

A guilty conscience
One day though, there was a Sam Haig with her, which indicates that this guy could be the "S" on the card. The episode ends with Merritt asking her kidnappers if she's trapped in there because of Sam Haig, and they tell her no. But even still, he's dead beecause of her. Just another person to add onto her conscience!
Elsewhere in the episode, Carl's personal life continues to be complicated as there's no progress in the case looking into who shot him, Hardy, and the officer that day; Jasper's mother Victoria shows up and gives Carl a lecture about sharing his feelings and opening up to Jasper; and we continue to see Carl's guilt over that day.
The only reason he's still alive and the bullet went through is because of where Hardy was standing and when the bullet entered his spine, it slowed it down where it wouldn't be fatal to Carl. He also is dealing with a guilty conscience.
Be sure to check out all of our episodic recaps of the series, here. Dept. Q is now streaming on Netflix.