Starring Vijay Sethupathi and Katrina Kaif, the film, set over the course of a night, revolves around two strangers whose lives get entwined after they cross paths at a restaurant on Christmas eve.

"The biggest enjoyment for me as a director was the way it shifted while scripting to editing, slowly from that hard-nosed thriller to this romance. Initially, I thought it would be a 90-minute thriller with no interval like ‘Ittefaq’. That was my thing. But as we fleshed it out, it changed for the better and the best.

"I’m so glad that we decided to shift the focus as we fell in love with these characters. It became a film about broken relationships and two broken people. Essentially, it is a love story, which is disguised like a thriller. That’s the big twist," Raghavan told PTI in an interview.

The 60-year-old filmmaker is happy that the film has garnered great reviews and the word of mouth is only getting stronger day by day.

"I’m getting a good response. Many people have seen it twice and it has touched them in a manner I didn’t expect," he said, calling the film a fun way to explore the spirit of Christmas through themes of "sacrifice and redemption" .

Raghavan, who in past interviews has spoken about how he wanted the story told within the span of a night like Yash Chopra's 1969 classic "Ittefaq", said he wanted to bring that intimate feel back by centering the story around two strangers just sitting and talking.

Raghavan even played "Ittefaq" for his unit as many had not seen the Rajesh Khanna and Nanda-starrer thriller that had this "cool man-woman attraction".

The film released on January 12 and had earned over Rs 13 crore at the domestic box office and the director hopes that it just grows in the next few days. His last release was 2018's "Andhadhun".

"We are expecting the second week to be good. Though many people were like, we came expecting this film to be like ‘Andhadhun’, but this happens with everyone after a successful film. I liked ‘Shaan’ as much as ‘Sholay’," he said, giving the example of the two Ramesh Sippy hits which released five years apart.

Known as the master of thrillers through films such as "Ek Hasina Thi", “Johnny Gaddaar” and “Badlapur”, Raghavan said the whole idea in designing his new film, based on Frederic Dard's famous French novel "Le Monte-charge", which also inspired the 1962 film "Paris Pick-up", was to keep the "audience invested".

"Today, people are hammered with so many big extravaganzas, which is great in their way, like watching an SRK film in a hall, it's superb. But 'Merry Christmas' is not like that. It's a much more intimate viewing experience.

"Here, the movie is about loneliness. Like, if you take a film like Martin Scorsese’s ‘Taxi Driver’, you don’t look at it like, 'Hurry up the pace' as you want to get to the climax. Cinema language is different. If they are in a cinema hall, the film has to captivate them,” he said, adding he tweaked many elements, including the climax, from the original novel.

Raghavan said he showed the film to Dard's family and they loved the way the movie has shaped up.

"He has written 300 books. He is like India’s Surender Mohan Pathak. He wrote pulp and about spies and all that. Somehow, four of his books were translated and I managed to get a copy of this book through a friend of mine. When I read it I thought, ‘We should make it into a film’."

Raghavan, a famous cinema nerd himself, is known for leaving clues and references of his favourite movies and novels in his films and "Merry Christmas" is no different whether it being a tribute to "Ittefaq" to his favourite filmmakers Alfred Hitchcock and French filmmaker Eric Rohmer. In fact, Rohmer's "The Green Ray" inspires a particular moment in "Merry Christmas".

In the opening credits of his latest film, Raghavan also tips his hat to Shakti Samanta, the director of hits such as "Howrah Bridge", "An Evening in Paris", "Aradhana", "Amar Prem" and "Kati Patang".

"There’s a beautiful scene in the opening of ‘Kati Patang’ where Asha Parekh screams. That’s a classic Asha Parekh expression (and also the opening of 'Merry Christmas'). We have dedicated the film to Shakti Samanta... He is almost forgotten today... I was like, it would be great to say 'hello' to him and remind people of this man’s legacy," the filmmaker said.

Raghavan's next is war drama "Ekkis", starring "The Archies" actor Agastya Nanda.