“A lot of my scenes were by myself, and I didn’t talk a lot in the first half of the film,” says Smith. “I had a lot of quiet time, and for whatever reason that helped me sink deeper into the pain of the loss. It’s a parent’s worst nightmare. You don’t want to imagine it.”

Collateral Beauty, directed by David Frankel (best known for directing The Devil Wears Prada) off a script by Allan Loeb (The Switch, Rock of Ages), is, however, not solely about the death of a child – which in and of itself is a pretty grim way to try to get people into the theatres. While there’s something of a fable-esque and even slightly surreal quality to it, the film is, at its core, a drama that has moments of levity while simultaneously begging the viewer to be profoundly moved.

When we first meet Smith in the film, he is Howard, a brilliant and charismatic Madison Avenue advertising executive who seems to have it all – until he is a dealt a blow that all but destroys him. He spends his days alone in a dingy apartment; when he does show up at the office, it is to build elaborate domino arrangements, which he then proceeds to topple down.

His advertising genius is predicated on his belief that people everywhere seek two things – time and love – and that they fear one – death. So he starts sending letters to those concepts as if they were real people.

Wedged into the structure is a secondary plot about the now-faltering company which Winslet, Edward Norton and Michael Peña need to save – and the only way they can do that is to prove that Howard is insane. So they hire actors pretending to be Time, Love and Death to reach out to Howard. A grief group, led by Naomie Harris, is critical. And there is a fair bit of leapfrogging between themes – something that Frankel was equipped to handle going into it.

“It was a process of exploration and we shot in every possible direction,” says Frankel, who was sitting alongside Smith, Mirren, Harris and Jacob Latimer (who plays Time) at a recent interview in West Hollywood.

The actors said they were all drawn to the conceit of Collateral Beauty. Smith says the project came to him at an interesting time: his father had just (wrongly) been given six weeks to live. (Smith’s eventually father died in early November). And that proximity to mortality helped the actor access the emotional range to pull his character’s distress off.

“I believe that up is inexorably bound to down, that light is bound to dark and love to pain. I think you can find all things in everything. There’s a quote in Paulo Coelho’s The Alchemist that says the whole of the universe is contained in a single grain of sand. For me, this idea of collateral beauty fits into that concept – that there is nothing that can happen that is all good or all bad. It’s both things, and all things, simultaneously.”

Mirren, who plays a stage actress in the film, said she was attracted to the role because of the way its characters strive to “find light in the darkness”.

“I was very taken by the script, by the essence of what the film is about,” she says. “I loved that idea because I see it in life and it’s such a beautiful thing about human existence. I love to see a film for the first time that really addresses that concept and in such an interesting way. It’s comedic but it’s far from a comedy. It’s entertaining. It’s a fable, but it’s realistic. I knew I wanted to be a part of that.”

Frankel agrees that the ways audiences might respond to the film will rest on how nuanced the transitions are between the lighter and heavier components of the piece, so much so that lengthy discussions were had over just how many tears needed to be shed.

“There is a board room scene, and in the first take, Will’s character cried and it was beautiful and moving,” the director says. “Will had prepared a lot for it. But I said to him, ‘We have another scene later when you’re going to cry, and there’s only so much crying this character can do in the space of this movie’. So we shot for another eight hours – without any crying.”

To help Smith get to the point of genuine tears, he would put on certain music, such as Sam Cooke’s A Change is Gonna Come. At other times, he gave in to the fear of losing those he loved.

“I had to come to grips with the idea of impermanence, to figure out how to gracefully let go and still continue to create,” he says.

“We have to be able to look at death and smile at whatever time we have left, to reach for love. It’s a really beautiful exploration. There are ideas in this film that when they reach people at the right time in their lives, it can be extremely healing. I think this movie has the possibility to be a lifeline in dark moments.”

Collateral Beauty opens on December 29

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