I feel like guest casting is a science. Score the right person in a role and you get gold. Nab the wrong person and it can ruin a storyline or episode. Motive has always been great at finding the right people to come and play; last season’s standouts for me were Brooke Nevin (Cracked) and Jason Dohring (Veronica Mars) both playing against type. This season Motive has been firing on all cylinders and Sunday’s newest episode was no exception.

“Oblivion” featured two veteran actors portraying characters opposite from what we’ve traditionally seen from them to great effect. Stephen Lobo, who often plays jerks—most recently as Kellog on Continuum—was the good guy this time around. His Isaac was fiancé/developer Isaac, who had his life turned upside down when Robin dumped him and disappeared. By the time Angie and Vega showed up at his office Isaac was beside himself with grief, wondering what had happened to the woman he’d loved so much. Shockingly, Isaac had nothing to do with the murder of Jeff Armstrong, a city planner who stood in the way of Isaac’s next project getting off the ground.

Instead, it was Robin herself who murdered Jeff by swapping out his scuba tank of oxygen for one filled with nitrous oxide. Former Gilmore Girls lead Alexis Bledel was simply stunning as Robin. She was cold and calculated in her dispatching of Jeff and at first I’d assumed she’d done it—and made like she’d been murdered to throw off the police—because she was so devoted to Isaac that she’d do anything for him.

But in a great twist, Robin and Jeff had once been together and a car accident had killed their unborn baby and rendered Robin sterile. Furious that he had moved on with his life—and that he was in the way of Isaac’s project going forward—she killed him. I was totally sympathetic to Robin and her feelings, and understood her rage at Jeff’s insensitive comment that she move on. It was easy for him to say—he had a baby on the way with his new gal pal while Robin could never conceive—and for once I cheered for Motive‘s murderer of the week.

Well done, Motive, well done.

Notes and quotes

• “I keep expecting original recipe Cross.”
• I like Vega’s new glasses. And though he passed the shooting test, I worry he’s got an eye issue that may jeopardize his career or put someone in danger.
• The slamming of that door into Angie’s desk cracks me up every time.
• “Helping a murderer. That’s love.” — Vega
• This Montgomery fellow seems like a bad dude.

Motive airs Sundays at 10 p.m. ET/PT on CTV.

Taking nothing away from what makes Motive such a compelling show—the crime and the guest stars—but so far it’s been the Season 3 relationship twist that has been entertaining me the most.

Heck yes I was thrilled to see Ally Sheedy and Bonnie Somerville in “Calling the Shots,” battling toe-to-toe over money invested in a Ponzi scheme that led to murder. Did I have a crush on both at points in my life? Why yes I did. (I still miss Somerville’s Kitchen Confidential.) Having Sheedy play Stephanie Carson, an uptight mom who viewed the death of Somerville’s Erica Gray as not only dispatching a rat but also helping further her own daughter’s chances at scoring a gymnastics scholarship? Immensely entertaining.

But it was the relationship between Angie, Lucas, Vega and Betty that had me grinning with pleasure the most. And why not, thanks to back-and-forth conversations like the following?

“The proof is in the pudding,” Vega opined to Angie upon learning a prison inmate was killed over the creamy dessert.

“The plot thickens,” Angie shot right back.

And later, during the murder investigation and subsequent clearing of a virgin who Erica had given the bum’s rush to meet with Stephanie: “Are you ready for this? They had rhubarb pie and watched Doctor Who,” Vega exclaimed to his partner. It’s exactly that witty dialogue that sets Motive apart from other shows in the genre and keeps me tuning in.

The cherry on top of this Sunday night confection is Lucas. It’s only taken the rookie detective six months to go from babbling young cop to confident crime-solver—four solves in four cases—something that has put Angie on her heels. She’s used to being the lead and not having to clear anything with Lucas. But now she has to, and it’s definitely going to be a learning curve. I hope her education continues so that we get more awkward morgue scenes between the four like we did this week.

Motive airs Sundays at 10 p.m. ET on CTV.