Warning: Disturbing content

The teenager was left for dead with her head caved in, cable-tied and unconscious after a meth-fuelled attack over a love spat, a jury has heard.

The Crown has opened its case in the High Court at Auckland against the five people defending a range of charges relating to an attack on a 19-year-old in Dome Valley, north of Auckland, last year.

Prosecutor Henry Steele told the jurors the woman was found lying in a patch of flattened grass where she'd been left for dead for 10 hours.

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"Her skull had been smashed with a hammer."

But the story of how the 19-year-old got there was long and complicated, beginning after one of the defendants, Nicola Jones, believed the victim had slept with her ex-boyfriend, Steele told the jurors.

Jones was furious and allegedly texted the woman's mother that if she ever saw her daughter, she'd kill her.

"Your daughter is history."

It was with the help of her friends - Julie-Ann Torrance and Cameron Te Hau Kareti Hakeke, also known as "Cinnamon" - that she got her revenge.

Hakeke lured the woman to his house under the guise of wanting to buy a "Q", quarter of a gram, of methamphetamine and there she was ambushed, Steele said.

She was then allegedly assaulted with Tasers and her hair was cut with scissors until she gave her assailants her car.

Torrance and Jones then allegedly drove the woman to a spot by the Bombay Hills, dropped her on the side of the road and told her if she ever came back to Auckland "she'll get more of the same".

Steele said the woman hitched a lift to her mother's place in Taupo then returned to Auckland.

On May 8, Jones, Torrance, Michelle Blom and Jaclyn Keates, who has admitted her charges and been jailed, saw the woman on Karangahape Rd after smoking meth at a party.

Jones allegedly dragged the woman back to the car, where she was punched and driven to a house on Great North Rd.

"And it's there where the fun really starts because this is what this is to them," Steele told the court.

This was the second time they'd allegedly kidnapped the woman in two weeks.

"They've got their plaything and they're going to have their fun."

The woman's hair was cut shorter, she was stripped naked and her left hand was stepped on and broken before she was sexually violated with a cricket bat, the prosecutor said.

At some point Wayne Blackett arrived and eventually "they tired of torturing" the woman so they bound her with cable ties, dressed her and put her in a balaclava before throwing her in the boot of Blackett's brother's ute.

They drove north to Dome Valley, stopping for pies and a cordon bleu at the BP station, and found the dirt Waiwhiu Conical Peak Rd where they dragged her out of the ute tray, the court heard.

Steele said an attempt was made to strangle the woman.

"When this doesn't work they attempt to break her neck manually like something out of a cheap kung fu movies."

But she was still alive. It was at this point her head was caved in with seven blows of a hammer, Steele said.

Before the Crown opened the case, Justice Christian Whata warned the jury they would hear some "very disturbing things" which allegedly happened to the complainant.

"Understandably you will feel very emotional about these things."

But he urged them to but their emotion aside and judge the facts of the case without prejudice or sympathy.

Whata told the jurors they would be given a document showing charges the defendants had already admitted.

However, if one person had pleaded guilty to one charge but another hadn't they "must not jump to the conclusion" the person defending the charge committed the offending.

"If a defendant has pled guilty to a charge you must not assume that he or she is guilty of another charge."

Everyone should be deemed to be innocent until they believed the Crown had proven the charge.

Each defendant was separately on trial for each charge.

"You are the judges."

The trial is set down for four weeks.

The charges the defendants face are:

Nicola Monique Jones, 29, of Tauranga:
Attempted murder, sexual violation, injuring with intent, assault with Taser, threatening to kill.

Julie-Ann Torrance, 42, of Henderson:
Attempted murder, sexual violation, assault with a cricket bat, assault with a Taser, assault with scissors, injuring with intent.

Wayne Edward Blackett, 39, of Manurewa:
Sexual violation, assault with a cricket bat, assault with scissors.

Michelle Blom, 30, of Glen Eden:
Kidnapping, sexual violation, assault with a cricket bat, assault with scissors, injuring with intent.

Cameron Te Hau Kareti Hakeke, 34, Green Bay:
Kidnapping, assault with a Taser, assault with scissors, robbing victim of a car, iPad, phone and other items.