Children’s author Helen Bailey was plied with sedatives and "probably suffocated" by her partner before being dumped in a cesspit below her home, a court has heard.
The 51-year-old writer was found deep in the grounds of her sprawling £1.5 million property in Royston, Hertfordshire, in July 2016, three months after she was reported missing.
Near her side lay the remains of her beloved miniature dachshund, Boris.
Ms Bailey's fiance, Ian Stewart, 56, of Baldock Road, Royston, is accused of killing her after he "secretly administered" a sleeping drug in increasing amounts over time.
Opening his trial at St Albans Crown Court, prosecutor Stuart Trimmer QC said: "The crown say this was simply a long-planned, deliberate killing, a cynically executed murder that had money as its driving motive."
Jurors heard that the killing allegedly took place on April 11 2016 at the home the couple shared, before Ms Bailey’s body was hidden in a septic tank below the garage.
Her death put the defendant in line for "substantial financial advantage", the court was told.
Stewart is charged with murder, three counts of perverting the course of justice, preventing a lawful burial and fraud.
He denies all the accusations.
On the day the author was allegedly killed, her bank account was accessed, with a standing order to the defendant bolstered from £600 to £4,000, the court heard.
Mr Trimmer said: "(The couple) had made financial arrangements that meant, in the event of the death of Helen Bailey before the wedding, Ian Stewart would obtain the house and a very substantial financial advantage."
At the time of her killing, Ms Bailey was said to be worth more than £4 million.
The victim was said to have been concerned in the weeks leading up to her death that she was feeling unnaturally sleepy.
"The crown case is that this defendant secretly administered to her a sleeping drug in increasing amounts," Mr Trimmer said.
He added: "All the typical activity that Helen Bailey engaged in ceased at about 11am Monday, April 11 2016 ... the crown case is that, by early afternoon, the only other person in that house, Ian Stewart, killed her, probably by suffocation whilst she was sedated by the drugs he had administered for some time."