In a case her lawyers say is a test of whether the French courts can deal fairly with people of unconventional sexual habits, Diane Mistler, 45, is appealing against a 25-year prison sentence for allegedly persuading her lover Frantz Diguelman, 45, to kill her husband.

The husband, Paul Mistler, 60 and a retired banker, was shot by a harpoon normally used for underwater fishing as he left a swingers club in the French Mediterranean resort of Grande-Motte with his wife in April 2007. He was then stabbed 20 times with a butcher's knife.

Diguelman was arrested shortly afterwards, hiding under a car in clothes soaked in blood.

Diguelman, a barman, claimed he had acted on Diane Mistler's instructions in the belief that her husband beat and raped her and forced her to prostitute herself as well as attending swingers' parties.

Police could find no evidence to substantiate that claim, which Diguelman only made six months into the inquiry, after he had discovered his lover had numerous partners and that their relationship was, for her, purely sexual.

The appeal court will decide whether Diane Mistler did in fact order her husband's murder, with her lawyers arguing that her conviction was the result of disapproval of her lifestyle rather than hard evidence.

"Fundamentally there is no case," one of her lawyers, Françoise Dalran, commented. "She was (seen as) a slut, so she was convicted."

Another lawyer, Jean-Robert Phung, added: "Diane couldn't be aquitted because she wouldn't admit to doing anything wrong, because she had 48 lovers, because she telephoned one while making love to another, because she wouldn't apologize for the life that she led."

Lawyers for Diguelman will argue that their client was manipulated by his lover and that he interpreted a comment from her that her husband could no longer "get it up" as a signal that she wanted him killed.

The prosecution says Diane Mistler wanted a divorce from the victim but feared her lifestyle would cost her custody of their son and believed that having him killed would be financially better for her.