Happy Valley's big twist was written on the wall

It was a moment of crushing devastation and acute confusion for the world-weary police sergeant, who never once suspected that her sister and closest confidante would have orchestrated the ultimate betrayal: "You think you know people..."

But she did cast doubt on Neil's character: "Clare and Neil have taken him to watch football matches when I've been working but... see Neil, I don't know about Neil. I've never been sure about Neil. But Clare? She just wouldn't, she wouldn't do that to me, would she?"

Tommy's shadow has loomed over Catherine following her daughter's suicide, which is tragedy enough for one lifetime, but his growing presence in Ryan's life, once a distant concern following his imprisonment, has mutated into an immediate threat – and Clare has played a part in facilitating that.

But her 'betrayal', while a gut-punch, shouldn't come as a surprise.

Catherine describes her sister as "weak" when confronted with the truth, and plenty of viewers will nod along furiously in agreement. This is Tommy Lee Royce we're talking about, after all. He raped Catherine's daughter Becky, which was the catalyst for her death and has committed several murders, among other nefarious, violent acts. He is a threatening, noxious presence, capable of destroying anyone and anything in his path.

But in a less abrasive light, the weakness that Catherine identifies in Clare can be construed as empathy, which is an intrinsic part of her identity.

While Ryan has effectively had two mums in Catherine and Clare, who have split parenting duties between them, the knowledge that his biological father is not only within touching distance but wants to be an active presence in his life would prove difficult to ignore, particularly at such an impressionable age.

It's impossible to know if Tommy's interest in his son stems from a genuine desire for familial connection, to satiate his own twisted fantasy of moulding Ryan into a miniature version of himself or to torture Catherine. It's likely all three but as far as Ryan is concerned, it's purely about building a robust father-son relationship and the allure of that would be overpowering for anyone, especially at 16 years of age.

And while Tommy did douse the pair of them in petrol and threaten to set himself and his son alight in the first season, he's since switched up his scheme. He's adopted a gentler approach that leans on emotion rather than spectacle, in part due to the constraints of being behind bars, but also because he's well aware that Ryan is no longer eight years old and one wrong move could alienate him – and it appears to be working given that the pair have met four times during the past year, with a helping hand from Clare and Neil.

Details about the specifics of Ryan and Tommy's arrangement, such as how it first came to be, are currently foggy – was it Neil who first orchestrated this? Is he a domineering presence in Clare's life? But we do know that Ryan chose to confide in Clare rather than Catherine because the latter would have outlawed any contact between her grandson and his father. She has displayed her fair share of empathy, both in uniform and out, but there is simply no budging here. Tommy will always be persona non grata.

But Clare is not her sister. Unlike Catherine, she has a more merciful tendency and is quick to dole out forgiveness if the person seeking absolution appears genuine, as demonstrated when she helps Ryan put his room back together following his confrontation with Rob Hepworth.

It's also important to remember that Tommy is a highly manipulative figure. After a number of years in prison, it's possible he's convinced Clare that he is a reformed man, guided by the Lord's light, in a bid to be the father that he himself was deprived of.

Clare's compassion is fuelled by her personal recovery from drug and alcohol addiction and Neil's own rehabilitation from substance abuse, plus her voluntary work at a local missionary, shaping her into someone who is able to reserve judgment. When you yourself have desperately sought exoneration for your missteps, however great, you can't help but extend the same courtesy to others, or at least entertain the idea.

And for it to be Ryan who asks this of Clare, likely making a strong case for why he deserves to speak to his father, and likely displaying raw emotion atypical in a 16-year-old boy, would be difficult to refuse. He's endured more than most during his short life to date and a chance to build a meaningful relationship with a parent after losing another so young gives his argument legitimacy, in spite of the potentially catastrophic outcome.

There's also the very real risk that refusal to support Ryan would drive him away, the Cawoods losing him forever, which would put him in an intensely vulnerable position. By monitoring his interactions with Tommy, Clare and Neil are able to ensure that he isn't cut adrift and submerged in Tommy's riptide.

And if we're viewing it purely through the lens of constructing compelling telly, it had to be Clare.

The closing scene, in which Catherine watched her sister feed her barefaced lies over the phone, was a masterclass in tension, with Wainwright's dialogue and the performances from Lancashire and Finneran coalescing to create a scene that was so mesmerising, I forgot to take a breath.

Three seasons in and Wainwright is still finding ways to dazzle audiences as she raised the stakes further ahead of the season's halfway point.

What now for Catherine and Clare's relationship? And does this prompt the "big showdown" between Catherine and Tommy?

Happy Valley season 3 continues on Sunday at 9pm on BBC One and BBC iPlayer. The first two seasons are available to watch on BBC iPlayer now.

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