Viewers were gripped to the tricky case between Laura (played by Joanne Froggatt) and Andrew (Ioan Gruffudd) as the former says she was raped but the latter says he is innocent.
The harrowing tale made plenty of twists and turns as the ITV drama drip-fed tiny bits of information to help them piece together the case.
However, with all eyes on the rape case, it seems that one small detail was missed as a character threatened to murder Andrew.
Laura’s sister, Katy, works with the hunky surgeon and was one of the driving forces encouraging the two lead characters to date.
But as she egged on her colleague, Katy warned Andrew: “If you hurt her, I’ll kill you.”
Although a throwaway line at the time, bosses behind the drama have promised that almost every character is hiding something.
As viewers should trust no one, will Katy make good on her promise and avenge her sister’s alleged rape.
This comes after episode one’s dramatic cliffhanger which saw the teacher come to the conclusion that Andrew drugged her by switching the wine glasses.
Although her memory is hazy from the night, Laura convinces herself that she has remembered the truth and outs Andrew as a rapist on social media.
But with five more episodes to go, fans have a long way to go before they discover who is really telling the truth.
Liar continues next Monday on ITV at 9pm.