BBC One's The Cry Finale Didn't Answer One Really Important Question

There's nothing pleasant about The Cry. Save for the beautifully picturesque locations across Scotland's mountains and Melbourne's beaches, BBC One's latest psychological thriller-cum-crime drama isn't meant to make you feel good. It's a story about a missing child, a crumbling relationship and the unravelling of a young woman's world. We had high expectations after Bodyguard, but I don't think anyone could've prepared for the emotional whirlwind that this month's Sunday night TV has provided.

It's fitting, then, that when it came to last night's fourth and final instalment of the series, we were left only half-satisfied. We're right where they want us – relieved that we'd made it through to the end still on Joanna's (Jenna Coleman) side and feeling somewhat vindicated by the outcome, but also just curious enough about those annoying little plot holes to draw us back for season two. Well played, BBC. Well played.

In the finale, those clever, disorienting jumps across the mystery's timeline were finally connected. Much to Twitter's relief, we found out that Joanna was standing trial in Scotland for the murder of her awful husband, Alistair (Ewen Leslie) – he convinced her that she had mistakenly given their son Noah the wrong medicine (which ultimately killed him) when in fact it was him all along. We also discovered how much of a manipulative, conniving and vile person he truly is. We witnessed the cause and effect of Joanna's complete unravelling. We finally identified that all-important turning point in Joanna's journey, and we connected to her pain even more.

And while the big questions about the missing baby were eventually answered – yep, Alistair lied about burying Noah beneath a tree he used to visit as a kid, instead burying him on the construction site of the new build that he would later suggest purchasing – there's a smaller but hugely significant question left hanging. Namely, how much did Alistair's mum Elizabeth know about what really happened?

When Alistair is packing, preparing to leave his mother's house and return to Scotland with Joanna to try and "rebuild their lives", Elizabeth enters the room and addresses him knowingly. She tells him that leaving Melbourne is the right thing to do. She tells him that one person can't possibly carry the the responsibility of "abducting" Noah alone. Alistair responds with "two people can keep a secret better than one" and there's something in Elizabeth's face that tells us she knows more than she's brave enough to say.

There's a real solidarity between the women Alistair betrayed, though. When Joanna wakes up in hospital, it's Elizabeth who is there to tell her that Alistair has died and that she is her family now. When on the stand and being questioned at Joanna's trial, not once does Elizabeth remotely insinuate that Joanna did or would do anything to hurt Alistair or baby Noah. Even Alistair's ex-wife Alex observes Joanna reservedly, as though she knows something about what really happened, too. And even though Joanna remains "the other woman" with whom Alistair cheated on her, when Alex takes the stand – an opportunity for revenge which many would seize – she's very much on Joanna's side.

As one Twitter user said: "Alex and Elizabeth not throwing Joanna under the bus every chance they got we stan women supporting each other." We're given the impression that there is something shared between them. A secret, or the truth, perhaps. Though the truth has been on the tip of Joanna's tongue for the majority of the episode, she doesn't reveal to the court what really happened to her baby boy and instead progresses with the yearlong lie about Noah's apparent abduction. In the final scenes it seems that her secret is safe – but how long for is up for debate. Between her return to Australia to live in the house built on top of her baby's grave, and Alistair and Elizabeth's 14-year-old daughter's unnerving commitment to the search, the entire case could unravel pretty quickly. If a second series is commissioned, it's got a very interesting place to start.