Fans of Channel 4's supernatural drama The Returned hoping for all the answers to its numerous mysteries will have to wait longer than its first series climax on Sunday.

The channel confirmed on Friday that it had bought the rights to the second series of the subtitled French drama, which has been one of the summer's unlikely hits. Such is the secrecy around the plot – centred on an Alpine town where the dead come back to life – that not even the cast have been told about the new series, which is due to begin filming early next year.

Les Revenants, as it is known in France, was the biggest ever original series to run on Canal+, part of the pay-TV broadcaster's efforts to turn itself into a French equivalent of US cable network HBO.

But the final episode of the first series, which aired in France at the end of last year, puzzled many fans. Some viewers took to Facebook to complain were "no answers to the questions raised by the intrigue". In response, the show's creator, Fabrice Gobert, hinted that explanations would come at the start of the series two.

The Returned is no ordinary zombie drama, said Louisa Mellor, TV editor of the Den of Geek website. "It's about our relationship with death, packaged in mad philosophy and loads of nudity in a way that the French do really well. Some of the most interesting elements are nothing to do with the supernatural – it's about depression, and the mother-daughter relationships. You don't have to be a zombie genre fan – in fact, probably the opposite."

As is often the case with hit overseas dramas such as The Killing and The Bridge (being remade in the UK as The Tunnel for Sky Atlantic), there will also be an English-language version of Les Revenants. Paul Abbott, the creator of Channel 4's Shameless, is developing a homegrown version with the working title They Came Back.

Jenna Thiam, who plays 19-year-old Lena in the French drama, confronted by the return from the dead of her twin sister Camille, said its theme was universal. "Nobody knows how they will deal with grief, and we see each character react in a different way," she told ES Magazine. "What was interesting about the part of Lena is that she rejects the situation completely. I think if it happened to me, if I lost someone, I would react in the same way if I hadn't finished grieving."

Based on a 2004 film of the same name, Les Revenants was given its distinctive feel partly by the director's decision only to film between 4pm and 9pm – "Fabrice always wanted it to be dusk", said Thiam – and by the eerie, distinctive soundtrack created by Scottish band Mogwai.

Channel 4 said a second series would begin filming in "early 2014" with an "anticipated broadcast later in the year".

The drama has been watched by a solid but not spectacular audiences on Sunday nights. Up against BBC1's The White Queen, it had just over 1 million viewers in the overnight ratings, increasing to around 1.8 million when recorded viewing over the following seven days is included.

But it was a bright point in a difficult summer for Channel 4, which earlier this month lost out to Channel 5 across an entire week's share of viewing for the first time in its history.

Channel 4's chief creative officer, Jay Hunt, said: "The Returned exceeded our expectations, both in terms of actual audience and their response to it. Having a quality subtitled drama in such a prominent slot enhanced our brand and is something only Channel 4 would do.

"There is a discerning audience who like to be challenged with beautifully directed, complex drama in a prime-time slot.

"We went for The Returned as we felt it was very Channel 4 in tone and if other shows come along which we think will resonate then we'll go for those. But we are not chasing every foreign language drama – it has to feel very us."