A property developer murdered his wealthy heiress wife in a holiday drowning "accident" to get his hands on a "vast fortune", a court has heard.
But less than three years later she was dead, David McLachlan QC told the jury as he opened the case for the prosecution in a trial expected to last up to six weeks.
Mr McPherson, born Alexander James Lang and originally from Auckland, New Zealand, denies murdering Ms Leeson on June 6, 2017.
The jury heard the defendant had a "big secret" - that in the four years before Ms Leeson’s death he had taken out seven life insurance policies on his wife, who was also to inherit a business worth "millions".
She knew nothing about the insurance policies on her life, but they were worth up to £3.5 million, all payable to her husband if she died first.
Mr McPherson, who also had a private pilot’s licence, had also forged her will, according to forensic handwriting experts, making him the beneficiary, it is alleged.
In June 2017, Mr McPherson and Ms Lesson went on a mini-break to a remote part of western Denmark, though her family noticed she was not herself and seemed "to have something on her mind".
While there she drowned in the swimming pool of the house they had rented, three days into the trip.
Mr McLachlan told the jury: "The prosecution case is, that whilst at first glance it appeared that her untimely death was an accident, the evidence will show that it was not.
"It was a sinister pre-planned killing and the person responsible for her drowning was none other than her husband Donald McPherson.
"The motive for the drowning was the oldest and simplest one in the book. It was financial.
"He stood to gain a vast fortune by her death. This was something which was not known by the Danish authorities in the immediate aftermath of Paula Leeson’s death".
Ms Leeson is said to have come from a close-knit, hard-working family.
Her father William "Willy" Leeson and mother Elizabeth "Betty" Leeson moved to Manchester in the late 1960s where they ran a family business, W Leeson and Son, specialising in ground works and skip hire.
They all worked in the family business, her younger brother Neville Leeson being the general manager and Ms Leeson overseeing invoices and the skip hire business - where she met Mr McPherson, who renovated and sold on property.
Ms Leeson had her only child, Ben, when she was 17 years old.
They all lived with their grandparents at the family home at Ashlands, in Sale, Greater Manchester, until Ms Leeson married Mr McPherson and they renovated their matrimonial home nearby.
Until she met Mr McPherson, Ms Leeson had a "relatively modest" pension and insurance policies.
Her husband had grown up with his parents and two sisters in Auckland, but claimed to be an orphan, "dumped" by his family to live with foster parents.
Mr McLachlan told the jury this was a lie, which was a "cover story" so he would never discuss his past.
Ahead of their marriage Ms Leeson made a second will, which the prosecution say was forged by her husband.
And two life insurance policies for Ms Leeson, each worth £400,000, benefitting her son, had a forged Trust form attached to them, diverting the cash to Mr McPherson.
Handwriting experts could not say who forged the documents, but Mr McPherson was the only person who stood to gain.
By 2016 the defendant was paying £464.47-a-month premiums for the life insurance policies he had taken out on his wife. He never missed a payment despite sometimes being overdrawn and "significantly in debt", the jury heard.
The trial continues.