The discovery of steamy love letters to a high-school sweetheart ended with a jealous husband daring his wife to steal a car to prove her love.

But when the couple took the vehicle home they panicked and wrapped it in plastic to stop their big dogs from scratching it. Details of the bizarre crime emerged during the trial of Ullricht Walter, 42, a German citizen who rents out classic cars in Cape Town, and his 41-year-old wife, Linda.

The deed, carried out "on the spur of the moment" while their marriage was heading for the rocks, saw both husband and wife convicted of theft in the Cape Regional Court in July this year.

A white Renault Clio was reported stolen from the V&A Waterfront in March last year. But the theft was captured by closed-circuit television cameras.

The couple, who are out on bail, pleaded guilty to a charge of theft and told the court that the car was stolen on a whim.

Ullricht said in an affidavit that neither of them were really thieves and that they took the car "probably because the keys were left in the ignition and the doors were left unlocked".

"I thought ... that if I gave her a task so outrageous and contrary to her nature it would prove to me and her that we would overcome our problems.

"I told her to drive off in the Clio to prove to me that she loved me and the children and that she had made a commitment to our marriage," he wrote.

Evidence led in court revealed that Linda had used the couple's own V&A Waterfront car parking ticket - issued when they drove their Mercedes-Benz into the parking lot - to take the Clio through security. Her husband simply reported his original parking ticket as lost, paid a R30 fine and drove off.

While the vehicle's owner, Elardie Mostert, feared the worst, her Clio was actually parked outside the Walters' home in Higgovale, an upmarket suburb at the foot of Table Mountain.

The following day, the couple drove the Clio into their back garden and wrapped it in plastic, "to protect it from being scratched by (their) big dogs".

Ullricht told the court they had intended to find the car's owner and return it.

Linda was arrested five days after the theft, when the police traced the car to their home. Ullricht was arrested on his return from a Namibian business trip a week later.

The court heard that Ullricht had discovered e-mail correspondence between Linda and her high-school sweetheart, who even flew out from Germany for a clandestine meeting.

Ullricht claimed in court that he no longer felt any "emotional connection" to his wife.

Linda had undergone sex therapy to improve their marriage, the court heard.

Ullricht testified that marital problems were uppermost in their discussions on the day they stole the car. "We had talked about staying together as a family, and Linda was yet to make a commitment."

In mitigation of sentence, the couple's legal team summoned criminologist Irma Labuschagne, who said this week that the case was "strange" but she had found no history of deviant behaviour in Ullricht or Linda.

The dare may have cost the couple their marriage. They moved out of their home and have lived apart since January.

Linda told Labuschagne that she might never be able to forgive her husband for what he asked her to do.

The pair return to court on October 27 for sentencing.