Tan Jianci in Lost, Indulgence

Tan Jianci is a dancer by training. The only scene that required him to dance in Lost, Indulgence posed a challenge: He had to move so badly that no trace of his grace and dexterity remained.

Lost, Indulgence is the 18-year-old's only film. He was 17 when it was shot last year in the hilly city of Chongqing. The scene involves him dancing to the music his father was listening to while his taxi rolled into a river.

It was set up to be the teenage son's expression of sadness at his dad's death and his frustration at being unable to track down the real cause of the accident, accentuated by the possible motive of showing off to a woman he has a growing affection for.

Tan complained about the slow tempo of the song, which was playing in the background. Once it was switched to a dance mix, Tan got the feeling and nailed the scene.

This is just one of several showy scenes in Lost, Indulgence, which opened nationwide on Nov 14. Although Tan has the meatiest role in the movie, there is a glittering cast: Jiang Wenli plays his hard-working mom; Eric Tsang has a cameo as his taxi-driver father; Eason Chan is the Hong Kong businessman who gets into a strange friendship with the mom, and Karen Mok is the mysterious woman who turns the family upside down.

"It was a learning experience," says Tan, whose character Xiao Chuan is caught in a vortex of conflicting emotions.

Tan was impressed with Jiang's attention to small details that she improvised during scenes.

"She would do something with her hair while talking to me, which added naturalness to a simple conversation between mother and son," Tan says.

Mok, the Hong Kong veteran, would remind him of the importance of blocking: "'Don't show the back of your head to the camera. It's your face that sells,' she would say, as I would be totally lost in the action and forget where I was in relation to the camera and other actors."

Director Zhang Yibai had a special way of preparing the freshman for his second Chongqing-based suspense-mystery movie, following Curiosity Kills a Cat in 2006. He did not tell Tan the whole story, but fed him scene by scene. "I knew I was to play an ordinary kid, but I did not know how the story would unfold until the preview," he says.

"I had a hunch by the end of the two-month shooting that something was going on between my character and Karen Mok's. But the director never told me it was an affair between a younger man and an older woman. I had always seen her as my older sister."

During the audition for the part, he was asked to give love notes to an elder sister-type actress, who tore it to pieces. And "I had to come up with different ways to plead with her, but she always gave me a hard time."

As soon as he arrived in Chongqing, director Zhang gave him 50 yuan and told him to go out and have a wild time. "I didn't know where I was in the city, it was getting dark and I was not allowed to take a taxi."

During shooting, Tan was encouraged not to socialize with other cast members. He was addressed by the character's name.

"Gradually I began to feel like Xiao Chuan and empathize with his loneliness and his yearning for human bonding," he says. "Xiao Chuan is miserable. Neither women, the older one played by Mok or a younger classmate, wanted him. He failed his college entrance exam. It was dawning on him that he was not good at anything."