When the contents of the bathtub first come into focus at the start of the premiere episode of “56 Days,” you’re not exactly sure what you’re seeing. It’s viscous, with a rainbow sheen not unlike an oil spill — and then you notice the skull and the skeleton and the goopiness of it all. But before you can ask, “Why is there a dissolved body in that fancy bathtub,” the calendar rolls back 56 days, and a new mystery begins.

It’s a strong opening for Prime Video’s new psychological thriller series, which loosely adapts Catherine Ryan Howard’s novel of the same name. And while it’s not without its faults, it mostly carries that momentum forward through its eight sexy, binge-worthy episodes.

Back to that body — or, well, what’s left of the body. The circumstances of what happened form part of the mystery of “56 Days,” particularly who the person was. That crime-solving-focused half of the story is told in one timeline, labeled “Today.”

The other timeline, which begins 56 days earlier and starts as “Day 1,” revolves around Ciara Wyse (Dove Cameron, as far from her Disney Channel days as possible here) and Oliver Kennedy (Avan Jogia, ditto his Nickelodeon days). The two insanely attractive strangers meet-cute while shopping for lunch — or do they? The chemistry is immediate, and so is the sex — both Cameron and Jogia, while overwrought at times, are absolutely smoldering here — but it’s obvious from the start that these two new Bostonians aren’t who they say they are. Why does Oliver have a new ID with a different last name? What do all those notes mean in Ciara’s notebook?

Each day that passes brings the answers a little closer to light. We learn how one mistake led to another, and to another, and then snowballed into this walking red flag of a relationship. (Seriously, who goes on a second date after catching the other in a lie during the first? Who moves in together after 10 days?!)

Most of the psychological thriller aspect of “56 Days” resides in the past; the present day, on the other hand, is all about mystery. Detectives Lee Reardon (Karla Souza) and Karl Connolly (a hilariously dry Dorian Missick) are tasked with solving the gruesome mystery that opened the series. They have their own secrets and backstories, but they generally fall wayside to the crackling energy between Ciara and Oliver.

Slowly (and at times unevenly), the two timelines begin to catch up to each other, and that’s where “56 Days” shines. The tension ratchets as bold text splashes across the screen, letting us know that we’re getting closer and closer to Day 56. The series is full of clever twists (some from the novel, many not), keeping you on edge as you wonder who’s in the bathtub — Oliver’s bathtub, mind you — and what will ultimately happen to the toxic couple at the center of the story. And it’s all amplified by a buzzy electronic and synth score that makes your pulse race.

Speaking of the novel, this series changes major elements throughout, including its setting (swapping COVID-era Dublin for current-day Boston). Most of the changes work, though a few feel shoehorned in, particularly a ham-fisted attempt to lecture about wealth inequality that only scratches at the surface of the problem. I won’t go any deeper, but expect to be surprised if you’ve read the novel.

“56 Days” can be a little silly, and it’s definitely heavy on the dramatics, but you can’t peel your eyes away as the mystery deepens. No one is who they seem, and it’s a delight to watch the layers fall away to reveal the core of who they are. It’s a messy process, for sure, but love, and murder, always are.

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'56 DAYS'

How to watch: On Prime Video Feb. 18

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