*SPOILER WARNING for those that haven't watched at least the Rajesh Khanna - Nanda film of Ittefaq, because I am going to discuss plot reveals*
The success and longevity of mystery plots is directly related to how well they are constructed: Stapleton must always be the arch-villain of the Hound of the Baskervilles, and no adaptation of Murder on the Orient Express will change its central solution. Elements may be modified and rearranged in reinterpreting them, but fooling around with the core is akin to disturbing the structural pillar of a tower; get too clever and it all comes crashing down. My memory of the original Ittefaq (how original? IMDB tells me the 1969 version was an unofficial "remake" of a '64 film called Signpost to Murder) is a little hazy since I watched it when fairly young, but the part where Nanda's hand is revealed hit home strongly because of how her character was portrayed till then - a frightened, disheveled overripe hausfrau who we could easily accept as a victim. Even her attempts to "seduce" the crazed intruder in her home were tinged with the perspective of a hostage desperate to escape her captor.
With the attractive promise of a short running time (104 min, identical to the predecessor?) and absence of song breaks Ittefaq '17 begins decently, setting up the core mystery fairly fast and adopting the Rashomon device of telling multiple POV narratives. I never understood the arbitrary "solve this crime in 3 days" deadline. It did not make sense in terms of the justification provided, nor did it add any specific urgency to the investigation. Logical leaps are acceptable in suspense stories when they are successfully masked by interesting character play and immersion. This is where Naya Ittefaq drops the ball on its toes. The Rashomon device requires a sophisticated level of deception and ambiguity (ask the makers of the much-reviled Basic). It is easier to accept a malleable truth between stories when there is a sufficient tonal consistency to show the plausibility of either facet. But the differing sides told by Sid Malhotra and Sonakshi Sinha are contrary to the point of caricature. In each perspective the characters behave in such archly different manner that neither tale appears credible.
As for the performances, what we have here is the result of either indifferent acting, incompetent direction or both. I recall saying around a year back "I have a soft corner for Sonakshi Sinha who I think is one of the promising actors of today..." Now I must eat my words with disappointment. Caked in enough pancake to make breakfast for the entire Kaurava clan, Sonakshi delivers a pedestrian turn that conveys little of her character's distress. Even in her own story, her reaction to a possible crazed killer in her house is akin to being annoyed with the Amazon delivery guy because the lahenga she ordered (COD, of course) arrived in the wrong color. Rajesh Khanna in the '69 film may be accused of hamming but Sid Malhotra's definition of restraint is a continually constipated stare, about as convincing and less entertaining. Akshaye Khanna essays the same character he did in Mom and once again suffers the penalty for the writers' laziness - Here he doesn't even have a Nawazuddin Siddique to play against, and his sleuth's swagger comes across as blowhard stupidity because the investigation is conducted in the most bone-headed way possible. Interrogation of suspects is an adjunct to objective forensic evidence, not a substitute for it, Sherlock Dev. As for the other characters, the less said the better. The cops appear to have been tutored at Keystone Academy and the writers' stabs (ha!) at generating casual banter are not worth the toilet paper that is the focus of one such scene.
And then of course, the TWIST. If the makers of Primal Fear got royalties for every time a movie took misbegotten inspiration from its final scene, they'd amass enough riches to smoke 100$ bill hand-rolled cigarettes for three generations. Once again, it's a twist that destabilizes the structure of the narrative, undermines everything you have seen before, and makes you feel a fool for having wasted your time on this Watdafaq.