They had dinner with friends at Merrylands Bowling Club, and got into their car to go home late at night.

About 1am on February 1, 2015, Mr Yarnton woke in the passenger seat and heard a "hissing sound" coming from an open gas bottle in the car, and found his socks soaked with petrol.

Ms Yarnton, 50, is now facing trial in the NSW District Court, charged with attempting to cause an explosion or fire with the intent to murder of Mr Yarnton???.

Married couple Monique Hayes, 25, and Fady Houda, 24, face the same charge, with prosecutors alleging they were part of the plot???.

All three have pleaded not guilty.

Crown prosecutor Guy Newton told the jury they would hear evidence the Yarntons were high-ranking prison officers, and Ms Yarnton found out Mr Yarnton was having an affair with one of their colleagues.

Tension and animosity grew as they separated, but continued to live together in their Menai home while it was being sold, Mr Newton said.

In January, Ms Yarnton went to a bank to request a $25,000 loan, telling the manager loan sharks were after her husband.

"Ms Yarnton was, prior to the event, trying to set up some records of some person being after her husband," Mr Newton said.

After the loan was granted, Ms Yarnton withdrew the money, and had a conversation with the bank manager.

"[Ms Yarnton] said words along the following lines: that she was counting down the days until she got the f---er out of her life. She also said words to the effect of 'I wouldn't care if he burned to death'."

During the Yarntons' final night out, Ms Yarnton bought her husband a beer, and security cameras captured her pouring it into another glass at the bar.

"[Ms Yarnton] put some substance in the drink with the intention of somehow making Mr Yarnton more drowsy," Mr Newton said.

When Mr Yarnton woke up alone in the car on Henry Lawson Drive at Picnic Point, finding gas bottles and petrol in and around his car, he called Ms Yarnton.

"She said she had no idea and said that she was going to the toilet, that she was defecating in the bushes. She said that she was lost and she was in the bush," Mr Newton said.

DNA allegedly matching Mr Houda was on a black glove found near the car, the court heard.

During police interviews, Ms Yarnton said she had no knowledge of the petrol or gas, but that Mr Houda offered to find someone to "kneecap" Mr Yarnton after Ms Yarnton told the young couple he was abusive.

Ms Hayes told police she had met with Ms Yarnton, who showed her a bag containing $20,000 cash, and asked her if she would kill Mr Yarnton.

The 25-year-old told police both she and Mr Houda declined.

But Mr Newton said there were message exchanges and phone calls between the trio on the night of the alleged attempted murder that appeared to discuss arrangements.

Defence barrister Michael Pickin told the jury Mr Houda denied any involvement. Mark Austin, for Ms Hayes, told the jury the trio were effectively facing separate trials and implored them to listen to all the evidence.

The trial continues before Judge Paul Lakatos???.