A teenage girl accused of killing an 84-year-old woman was quizzed about a murder manual found in her prison cell, a court has heard.
Anne Mendel was stabbed during a burglary
But Kemi Adeyoola, 18, told staff the 18 pages detailing how she would kill an elderly victim after robbing her was just "a story".
She is accused of stabbing Anne Mendel 14 times during a burglary at her home in Golders Green, north-west London.
Miss Adeyoola, of Camden, north London, denies murdering Mrs Mendel last March.
'Defensive and arrogant'
The prosecution alleges former neighbour Miss Adeyoola plotted a murder while at a young offenders' institute in Essex.
When questioned about the notes at the Bullwood Hall centre in October 2004, Miss Adeyoola claimed she was writing a book.
"She was defensive, arrogant and assertive," forensic psychologist Lydia Sear told the Old Bailey.
"She was asked: 'Is this something you are going to do?' She said: 'I want it back - it's a story'.
"There was concern what was behind it. She would not explain herself."
In police interviews, she said she got the idea of writing a thriller after reading American author James Patterson.
The manual detailed how she wanted to lose four stone in weight, make £3m and needed guns, knives and bullet-proof vests.
She described how she would kill an "elderly and defenceless" victim after robbing her, the court heard.
Detailed plans described cutting up the body and placing the bits in dustbins.
She also talked of cutting her victim's throat, placing the body in a car, setting it alight and sending it over the Dover cliffs.
The prosecution claims Mrs Mendel's murder may have been a dry-run because she was not wealthy.
Miss Adeyoola was arrested after her blood was found in swabs taken from Mrs Mendel's body.
She claims it got there the previous day when she helped Mrs Mendel across a road.
A 16-year-old girl, who cannot be named for legal reasons, denies two charges of perverting the course of justice by trying to arrange a false alibi for Miss Adeyoola.
The case continues.