Buckle in, the new episodes of Baptiste see the French detective face his most complex case yet. Georgia Humphreys finds out more from its lead star.

Tcheky Karyo may be almost 70 years old but, he insists, he feels like he's 30.

And it's a good job really, seeing as the final series of BBC's Baptiste - in which the French star plays the titular character - had plenty of action for him to get his teeth into.

"It starts with a big fight with the police, and this was a nice challenge, to do this fight with those young guys," enthuses the actor and musician, who was born in Istanbul.

"I'm happy to show that even if he's at the bottom of himself, he still has a lot of energy, and he is able to fight. I really enjoy being able to express that."

By "bottom of himself", father-of-two Karyo is referring to the fact his character, retired police investigator Julien Baptiste, has gone through a personal tragedy.

In the first episode of the new series - which is a spin-off from BBC hit The Missing - Julien has pushed his wife Celia (Anastasia Hille) away and is finding relief at the bottom of a bottle. What he needs is a new case to distract him - and then it turns out Britain's ambassador in Hungary, Emma Chambers (Killing Eve's Fiona Shaw), needs his help.

Her whole family has disappeared in the Hungarian mountains, so he travels to the resort where she's staying to use his experience and capacity for understanding human nature, to help her try to get her family back.

But there is lots getting in his way - buried secrets, a police force he cannot trust, and the media - who are obsessed with getting information on such a high-profile, international case.

"At first, Emma is a bit surprised by this stranger," Karyo, 67 - who's married to French actress Valerie Keruzore - elaborates on the storyline. "Julien's not afraid to trespass and is perhaps a bit delusional.

"In the despair that Emma is going through, Julien brings something magical, a different type of hope, and that helps to shake the rut they are in with the case. Emma admires his determination, his stamina, and his complete involvement in the situation. He won't give up.

"There is an exchange between Julien and Emma, where she is reminiscing on how she ended up in this situation and laughs at her misfortunes, but Julien admires that Emma hasn't blinked or broken stride, despite her situation."

He calls the ambitious second series "a very positive challenge, a very exciting adventure for me, to meet actors like Fiona Shaw, who is so amazing in the way she gets involved in her job. She doesn't take things for granted, she's always questioning, so it becomes a real dance".

He adds it was great working with Shaw because they are more or less the same age, and have both done a lot of theatre work in their career.

"I also appreciate that despite being from such different origins - she is British, I'm French - we have the same cultural references. She knows the same people I know in France and we had that as our middle ground. It was moving and there was something quite dear in meeting Fiona. I really love her!"

Baptiste is written by Harry and Jack Williams, the duo behind Two Brothers Pictures, who have also created dramas such as The Missing, Liar and Cheat in recent years.

"What I really enjoy with those two writers, is they don't forget to have humour and irony.

"They don't forget that life is not a tragedy, or a comedy - it's a tragedy-comedy. And they play with this strength."

This series in particular, notes Karyo, is about "society and how we explore different cultures and idealisms".

"When I read it, I thought it was really bold, because they are questioning society. How do we deal with the fear? How do we deal with this world we are going through today?

"They are working with and playing with immigration problems. How do we cope with different people? How do we cope with minority? How do we try not to lose our mind and be narrow-minded?"

There are many detective characters on our screens, but Karyo has gained a legion of fans since taking on the role of Julien - he has been hailed as a sex symbol, something he chuckles at and calls "a great feeling".

What he admires most about his character is his instinct.

"He's not formal and he's able to walk on the wild side. He's able to listen to people. I feel I could be good friends with Julien.

"I've played the character of Julien Baptiste over nearly eight years now. It's so special for me, it's one of the best experiences I've had as an actor, working with the wonderful production, and I have a lot of affection for them. It feels like a reward, because everyone is so bright and so humble and so talented. For me as an actor, it is so rich."

As for what's next, he "would love to play a character where I have to deal with the younger guy" because he thinks "it's interesting to question the difference of generation".

"It's interesting to question characters - for instance, an older man that wouldn't be able to deal with the younger one, because he would be feeling fear, or wouldn't want to understand that this young guy has maybe more experience than him."

For now though, he just hopes audiences enjoy going on a "roller coaster" watching these final six episodes of Baptiste, in which they follow Emma and Julien going through turmoil and dealing with corruption.

"There's a lot of twists and surprises," he teases. "The series will also provide a lot of food for thought about how one would deal with this kind of situation.

"They will also have fun, as there are humorous moments. Harry and Jack Williams are good at interweaving aspects of human life into these scenarios."

The final series of Baptiste will air on BBC One on Sunday, July 18, with all episodes available on iPlayer that day.