Serena Williams' (search) first dramatic acting part was challenging enough.

But when her eldest sister was murdered with one day left on Serena's shooting schedule on the set of "Street Time" (search) in Toronto, her novice's acting skills were really put to the test.

And she passed with flying colors, says Marc Levin (search), executive producer of "Street Time" and director of the episode in which Serena guest-stars as a former member of a girl gang who is just released from prison. The episode airs tonight at 10 on Showtime.

Serena began work on "Street Time" on Monday, Sept. 8, and had completed the bulk of her scenes by the following weekend, when tragedy struck.

Her sister - Yetunde Price, 31 - was gunned down on a Los Angeles street a few minutes after midnight Saturday.

Serena, 22, and another sister, Lyndrea, who had accompanied Serena to Toronto, got the news in their hotel room in the wee hours of Sunday morning, Sept. 14. "She came and told me at 6:30 in the morning," Levin recalled. "So I just got them out of there and got them on a plane."

When she left, Serena still had several minor shots to complete, but Levin told her he could work around that.

To his amazement, she insisted on completing her work on the gritty series about parole officers and ex-cons, returning to Toronto 10 days later on Wednesday evening, Sept. 24 to shoot her final scenes. He said her return to the set allowed her to say good-bye properly to the cast and crew members with whom she had become close, particularly series stars Scott Cohen and Erika Alexander.

Working with her "was a thrill," says Levin, a tennis buff. "There's a depth there and an intelligence and a sensitivity that I guess I just wasn't aware of. I was touched by it."