Two men and the infertile woman to whom they were "devoted" allegedly arranged to slaughter a vulnerable Victorian mother-of-four living in their backyard bungalow.
Former lovers Christine Lyons, 47, and Ronald Lyons, 45, who are not related, faced a Supreme Court of Victoria trial on Monday after allegedly agreeing to murder Samantha Kelly.
Prosecutors alleged the Lyons and her current lover Peter Arthur were motivated to murder so Christine, who "desperately wanted children", could become mother to the dead woman's offspring.
Ms Kelly, who had attended special needs schools as a child and still received support as an adult, and was "financially and emotionally vulnerable", had four children aged 11 months to six years.
The 39-year-old was living in a bungalow at the back of the Bendigo house which the Lyons and Arthur co-habited along with Ronald's three children.
The court was told there was no dispute that 46-year-old Arthur had delivered six to seven fatal blows to Ms Kelly's head with a hammer on the night of January 22 or the early hours of January 23, 2016.
But the Crown alleges the Lyons, who have each been charged with attempted murder and murder, and Arthur were in on agreement that Ms Kelly should go "on a permanent holiday".
The court was told on January 20, Christine Lyons went to a GP and obtained a prescription for the sedative Temazepam.
It is then claimed she planned to kill Ms Kelly by overdose, feeding her a "cocktail" of sedatives, beta-blockers, anti-nausea tablets, analgesics and antihistamines.
Christine and Ronald Lyons put the pills into a drink and gave it to Ms Kelly, who felt groggy but did not die, crown prosecutor Fran Dalziel told the jury.
They then gave her more tablets, telling her the medicine was to make her feel better, but in truth it was to give her an overdose, Ms Dalziel said.
When Ms Kelly still was not dead the next day, Arthur went to the bungalow and murdered her, the court was told.
It is alleged Ronald Lyons bought two shovels from Bunnings and accompanied Arthur on a trip to bury their victim.
The Crown says the trio told police Ms Kelly had left in the middle of the night with a man, had abandoned her children, and had wanted to "sign over" two of her children to Christine.
"Christine Lyons had a powerful desire to have a family, to have children of her own, and the two men ... wanted to give her what she desperately wanted," Ms Dalziel said.
"Both men were devoted to her and they knew she desperately wanted children.
"They were all part of an agreement or understanding under which they understood Samantha Kelly would be killed."
But the Lyons' defence barristers, Peter Kilduff and Jarrod Williams, said Arthur acted alone and the Lyons were not "complicit", nor were they part of an agreement to murder Mr Kelly.
The trial continues.