The Crown says Amandeep Kaur and Gurjinder Singh wrote love notes to each other but they also wrote notes planning the murder of Ms Kaur's husband.
Davender Singh was found dead in his car in Papatoetoe in August 2014.
His wife, Ms Kaur, and the man she was having an affair with, Mr Singh, have both denied charges of murder and have gone on trial in the High Court in Auckland.
Crown prosecutor Natalie Walker said notes written by the pair showed they planned where, when and how to murder Davender.
She read several examples:
"The Crown says the notes show an awareness of the need to be careful about not being seen on camera, not being observed by police and not leaving any fingerprints.
"For example: 'You're saying when we reach there, how will you kill and how will we come back? Who knows if there happens to be cameras? Do you have anything we can use to kill him? There is a lot of police around there. Please explain in detail so I can also be thinking in detail. Try to understand'."
To the outside world, Amandeep Kaur and Davender Singh's marriage appeared happy, she told the court.
It was an arranged marriage that took place in 2002 and the pair travelled to New Zealand five years later, leaving their child with family members back in India, Ms Walker said.
Friends described the marriage as happy, but all was not well.
Ms Kaur and Gurjinder Singh worked together at a plastics factory. Over just a couple of months last year, they shared 130 calls and sent 1000 text messages to each other.
After he found out about the affair, Davender Singh insisted that his wife carry a voice recorder - which he listened to every night.
At this point, Ms Kaur and Gurjinder Singh began writing notes to each other. The Crown said it was these notes that documented the planning of a murder.
The murder took place on a street, Ms Walker said. After Davender Singh picked his wife up from work, the Crown said Gurjinder Singh followed in his car.
He walked up to the driver's window, which was when the attack happened, Ms Walker said.
Davender was stabbed 13 times, including having his throat cut, she said.
Afterwards, Ms Kaur waited three minutes but Ms Walker said she did not call the police or an ambulance; she called a family member.
She said a stranger had stabbed her husband and stolen his phone, Ms Walker said.
But later, when confronted with evidence from a CCTV camera, she confirmed to police she knew the attacker was Gurjinder Singh. She also admitted she had had an affair.
It was not long before police caught up with Gurjinder Singh, too.
During a break in his police interview, he told his wife he was being set up by Ms Kaur.
In an unusual turn of events, the police allowed Gurjinder Singh and Ms Kaur to talk to each other with officers present.
Both agreed to take the blame before turning on each other and blaming the other one.
Gurjinder Singh said it was Ms Kaur who struck first, and that she held her husband's hands during the attack.
The Crown's case is that they did it together and both are equally responsible for the murder.
Gurjinder Singh's lawyer David Niven gave a brief opening address and said his client did not stab Davender Singh and had no idea anyone else would either.
The knife in court may not be the murder weapon, he said.
Ms Kaur's lawyer Sanjay Patel said his client withdrew from any plan to kill her husband after the pair reconciled.
She had told Gurjinder Singh that she did not want Davender to be harmed, he said.
The trial will hear from 55 witnesses and has been set down for five weeks.