May 23, 1994 12:00 PM

FOR 21-YEAR-OLD JEN BERGGREN, LIFE was beginning to resemble an upbeat ’70s TV series, one part Little House on the Prairie, one part The Partridge Family. Three years ago, from her close-knit family’s home on the woodsy fringes of Göteborg, Sweden, Jenny, her singing siblings Malin, 23, and Jonas, 27, and hometown friend Ulf Ekberg, 23, launched Ace of Base. Now Sweden’s hottest rock quartet since ABBA, the band’s perky pop sound rules the record charts in 10 European countries and the U.S., where the group’s No. 1 debut album, The. Sign, has sold 3 million copies. But Jenny’s enjoyment of her group’s stunning success has been shattered by a bizarre encounter with a disturbed fan at her parents’ comfortable suburban home late last month. “There is,” she says with brave understatement, “a downside to being a rock star.”

At home during a brief interlude from Ace of Base’s touring schedule, Jenny was asleep in a downstairs bedroom on April 27 when she awoke shortly after 4 a.m. to find a German-speaking woman hovering over the bed holding a large hunting knife. “I thought I was dreaming,” says Jenny, who quickly realized she wasn’t. “I tried to remain calm. I didn’t scream but said [in German], ‘Oh, you really scared me.’ “With that, the intruder grabbed Jenny by the hair, held the knife to her throat and blurted that she was an Ace of Base fan. “She said,” Jenny recalls, “she wanted to meet us.”

The woman then forced Jenny at knifepoint into her parents’ upstairs bedroom, where her schoolteacher mother, Birgitta, 54, leaped out of bed and “threw herself at the woman,” says Jenny. Explained Birgitta: “My first thought was that the woman was mad and I had to get the knife away from her fast.”

Stabbed in both hands during a brief scuffle, Birgitta forced the intruder to drop the knife. While Jenny’s father, Göran, 54, a doctor, restrained the woman, Jenny called the police. “Just before they took her away,” Jenny says, “she gave me a parting hug.”

The Berggrens now believe that the woman, who is being charged with assault and unlawful entry, had stalked the family for a week, lurking near the house and sleeping in adjacent woods. It was the same woman, reported to be Manuela Behrendt, 21, from northern Germany, who, they think, had earlier deflated the tires on their car and cut their TV cable. Encountering Behrendt outside the house days before the assault, Birgitta had even given her some apples and a fan club membership card. “I guess we were extremely naive,” says Jenny, whose parents have since installed a security system. “But our fame is very new to us, and we weren’t aware of all the problems of being rock stars.”

There are certainly no dark forebodings in the cheery pop music the Berggren kids began creating in 1991 when they teamed up with Ekberg to form Ace of Base. While the Berggrens were raised on classical music and Jenny and Malin performed in the local church choir, Jonas and Ekberg—the son of a tennis coach and his wife—shared a passion for synthesizer-based dance music. With the sisters providing the vocals, the group recorded their first album in 1992. After scoring a string of hits in Europe, Ace of Base sent two hummable, reggae-flavored singles, “All That She Wants” and “The Sign,” to No. 1 in the U.S.

But on the eve of Ace of Base’s first promotional visit here, the group has had to come to grips with the darker side of celebrity. “I still shake,” says Jonas, “when I realize my sister and my parents could have been killed.” Jenny, who now travels with a bodyguard and flinches when photographers’ strobes go off, is doing her best “not to freak out,” she says. “I’m still a little jumpy and I don’t want to sleep in a room by myself. But I’ll try to smile because I realize how lucky 1 am. I guess I know what life’s about now.”


JOEL STRATTE-MCCLURE in Monte Carlo and MARY JOHNSON in Stockholm