A man who had wife-sharing fantasies asked his colleague to have sex with his own wife, and both men toyed with the idea without ever talking about whether the woman consented to this.

When the opportunity came along two years later, the 48-year-old husband invited his 45-year-old colleague to his bedroom, where his wife of 23 years was lying on the bed.

The 44-year-old mother of three was naked, blindfolded and unconscious from alcohol and an unknown drug.

Fortunately, she regained consciousness before the man was able to rape her.

Yesterday, in a case described by prosecutors as "unprecedented" and "appalling", the colleague, who is now 47, was sentenced to three years' jail after he pleaded guilty to an attempted conspiracy with the husband to commit rape.

The offence carries a maximum jail term of five years. A second charge of molesting the victim was taken into consideration.

The parties cannot be named due to a gag order to protect the victim's identity.

The colleague is the first of seven men to be dealt with in a sprawling case where four husbands are accused of conspiring with other men to rape their wives between 2010 and 2018.

Four of the seven men are slated to plead guilty next month. They include the husband in the current case, who is accused of raping a 32-year-old woman in 2013.

Another of the men is claiming trial, while the last man has yet to finalise how he intends to plead.

In the current case, the High Court heard that the two men became acquainted in 2010 when the accused, a sales manager, supplied goods to the husband's workplace.

After they became colleagues in 2015, the husband started sharing details of his and his wife's sex life, as well as his fantasy of watching another man have sex with his wife.

The husband broached the idea of the accused having sex with his wife and the accused did not object to it.

On the evening of Aug 31, 2017, the husband contacted the accused and told him his wife was ready; he told the accused to come and watch as he and his wife had sex.

The accused arrived at the couple's home past midnight and was given access by the husband, the court heard.

The couple's children and maid were asleep in another room.

At first, the accused stood by while the husband fondled his unconscious wife. The husband then signalled to him to rape her as they had discussed previously.

The accused, who was later diagnosed with erectile dysfunction, tried to have sex with the woman but was unsuccessful.

She began to regain consciousness, and when she realised that another man was trying to have sex with her, she tried to remove the blindfold.

The man fled. The woman later managed to confront him, and made both him and her husband write confession letters.

The case came to light when another woman lodged a police report on Jan 2, 2020, after she found explicit photos of herself in her husband's phone and suspected that he and others had committed sexual offences against her.

This woman's husband was arrested and police established the identities of his accomplices, including the husband in the current case.

This in turn led to the arrest of the accused on Jan 10, 2020.

Deputy Public Prosecutor Chee Ee Ling sought between two and 3½ years' jail for the accused in the current case.

The DPP said: "Although (the husband) masterminded the perpetration of these heinous acts, the accused was crucial to the successful execution of the duo's perverse plans.

"The accused... breached the sanctity of her home, destroying her personal sense of safety and security and compounding the harm caused to the victim."

She also noted that he was convicted in 2018 for sexual offences, including four counts of insulting the modesty of women.

Defence counsel Nakoorsha Abdul Kadir asked for between two and 2½ years, saying that his client had written the confession letter the day after he was confronted.

He said the two men, unlike what the prosecution had alleged, had not planned the rape over two years and were just sharing fantasies.