A woman accused of murdering her husband and her lover's wife played an active role in a joint plan to kill for "selfish ends", a Crown lawyer said.
He was outlining the prosecution case in the trial of Hazel Stewart, 47, who denies murdering Trevor Buchanan, 32, and Lesley Howell, 31.
Their bodies were found in a fume-filled car in Castlerock in May 1991.
Former dentist Colin Howell has already pleaded guilty to the charges and was jailed for 21 years.
Mrs Stewart, from Ballystrone Road, Coleraine, denies the murder charges.
At the time, it was thought that the two spouses had died as a result of a suicide pact.
The fact that they were murdered only came to light two years ago, when Howell, 51, confessed to the killings following a discussion with members of his Church.
Howell confessed to gassing them while they slept in their own homes before driving the bodies to the house of his wife's late father and staging an elaborate scene to make it look as if they had taken their own lives.
The Crown lawyer told Coleraine Court on Tuesday that the murders were "a joint plan discussed in advance" by Mrs Stewart and Howell.
He said the killings were carried out "for their own selfish ends".
"We say that Hazel Stewart knowingly entered into this agreement and assisted Colin Howell in ensuring he could safely kill her husband and afterwards they both covered up the whole thing," he said.
The prosecution told the jury about a series of interviews given by Mrs Stewart when she was arrested in January 2009.
The prosecution said her account changed over a series of interviews over three days.
Firstly, she told police that she did not know what Howell was planning to do in May 1991.
"It was his plan," she told detectives. "I didn't want to know."
But she later acknowledged that she had opened the garage door to let Howell drive in with his dead wife in the back of the car, and that she had heard a struggle and had got clean clothes for her dead husband's body before destroying the pipe used to poison the victims.
She said she did this because Howell asked her to, adding that he was very controlling and had her in his "psychological" grip.
She denied drugging her husband and she said she did not cry out because she feared for her life and for those of her two children who were asleep in the other room.
She said she had lied to protect her children and herself.
Mrs Stewart also told police that she saw Howell in secret after the funerals and continued to do so for up to five years after the killings. However, she said the only reason she did this was because she was afraid of him.
The trial is expected to last for four weeks.