The six-part Australian programme, starring Downton Abbey actress Laura Carmichael as shop worker Aggie, is currently airing twice weekly on BBC One.
And Tuesday (July 14) evening's instalment had those watching at home more than a bit stirred up.
Warning! Spoilers ahead
However, it also had some scratching their heads as they wondered about the identity of one of the key characters.
In episode four of The Secrets She Keeps, Agatha - having faked a pregnancy and stolen the baby of lifestyle blogger Meghan (Jessica De Gouw) - horrifically killed Nicky, whose identity has been somewhat shrouded since episode one.
She followed him to a train station platform, where she lurked behind him - only to shove him onto the tracks just as a train was screeching into the station.
Viewers were gobsmacked and many had to admit that they didn't see it coming until the final moment.
Many others, however, were deeply confused over who Nicky was. A number shared the theory that he was her step-father.
What did viewers say?
One viewer wrote on Twitter: "So, she had one baby taken away from when she was raped, and then Chloe died in late pregnancy and Nicky was the father? Have I got that right? #TheSecretsSheKeeps."
Another asked: "#TheSecretsSheKeeps so was Nicky Aggie's stepfather?"
A third tweeted: "Who is Nicky? I'm confused #TheSecretsSheKeeps."
Someone else said: "#TheSecretsSheKeeps so was Nicky Aggie's stepfather?"
Nicky is actually Agatha's ex-husband and the father of her stillborn child, Chloe.
She killed him because she feared he would reveal her secret to her mum.
In the scenes leading up to his death, Agatha met Nicky at a cafe - and he appeared to be more than a bit suspicious.
When he asked where she had her baby, Agatha said Sydney, so Nicky said: "Oh? Someone said something on Facebook about Katoomba?"
"Yeah I had him in Katoomba and then came back here," she replied, barely keeping herself together.
"You know," Nicky continued. "The supermarket you're working at? It's practically round the corner from where baby Ben's parents lived... strange coincidence..."
She admitted it was and got up to leave. When they hugged, he hissed in her ear: "Your mum must be thrilled. I'll call her and congratulate her."
- The Secrets She Keeps continues this Monday (July 20) at 9pm on BBC One, but is available to watch in full now on iPlayer
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