Although Happy Valley fans know full well that Faisal Bhatti (Amit Shah) was the one who killed Joanna Hepworth (Mollie Winnard), it's clear to see police officers strongly suspect her abusive husband Rob Hepworth (Mark Stanley). Viewers were left repulsed by the emotional and physical abuse inflicted on Joanna by Rob, to the extent that she herself was willing to commit murder to escape.
When Joanna's body was discovered stuffed in a suitcase in the Hepworths' garage, seasoned officer Catherine Cawood (Sarah Lancashire) was quick to put two and two together, and things weren't exactly looking good for Rob.
For now, at least, it would seem the finger of blame has passed by corrupt pharmacist Faisal completely, with Rob set to take the wrap. There could however be one person who could help him prove his innocence.
This third and final season has had more of a focus on the now-teenage Ryan Cawood (Rhys Connah), who has reached a crucial crossroads in his life. Amid the drama over his murderous biological father Tommy Lee Royce (James Norton), Ryan has also had to deal with issues at school, having become the target of bullying PE teacher Rob.
Joanna, herself a former pupil of Rob's, had been aware of her husband's pattern of picking on a certain boy at school, before trying to help them in order to seek control. Although his motive for this behaviour is currently unclear, this very much fits with his treatment of Ryan, who he appears to have singled out to belittle.
On the day of Joanna's brutal murder, however, things appeared to take a turn in the dynamic between Rob and Ryan, with the teacher expressing concern for Ryan's family difficulties and precarious living situation.
Encouraging him to open up, Rob even apologised for having been so hard on him, admitting he hadn't known the complicated situation Ryan had been dealing with at home.
Whether or not this was just part of Rob's pattern of gaining a pupil's trust after breaking down their confidence remains to be seen, however, some believe this conversation could prove to be far more important for the larger plot.
At around the same time Faisal was murdering Joanna in her own kitchen, suspect number one Rob was seated with Ryan in the gym, having a heart-to-heart.
Given his uncomfortable history with this teacher, it's fair to say this is the sort of out-of-character chat that would stick with Ryan, despite all he's going through outside the school gates. Some now believe Ryan's recollection of the conversation could provide Rob with an alibi, and ultimately prove his innocence.
In a Reddit forum dedicated to such theories, one eagle-eyed fan wrote: "Police will work out the time of death on the dead wife and the husband's alibi will be Ryan as he was talking to him in the gym at the time."
This possible alibi plot point makes a lot of sense in terms of showing Ryan's character development, all while highlighting how he is ultimately far more similar to his grandmother Catherine than the psychopathic Tommy.
During an earlier chat about Rob's unprofessional behaviour, Ryan declared that revenge was 'a dish best served cold', a turn of phrase it's easy to imagine coming out of Tommy's mouth.
Catherine on the other hand drily cautioned him to just get used to having to deal with difficult people, as this was simply a fact of life.
By providing an alibi for the teacher who bullied him, Ryan would be showing himself to be the bigger person, a far cry from cruel Tommy's vengeful inclinations.
You can catch the final ever episode of Happy Valley on Sunday at 9 pm on BBC One and BBC iPlayer.
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