A teenage jihadi bride plotted a terror attack on London under the guise of an Alice In Wonderland themed tea party, a court has heard.
Safaa Boular was aged 17 when she allegedly decided to be a "martyr" and launch a grenade and gun attack on the British Museum.
Her resolve was strengthened after her Islamic State fiance Naweed Hussain was killed in Syria before she could join him.
While in custody for allegedly attempting to travel to IS territory, she passed on the baton to her older sister Rizlaine Boular, the Old Bailey heard.
In calls from jail, she talked about a "party" with her 21-year-old sibling, which was said to be a code word for a terror attack.
The pair also made reference to a "Mad Hatter" and having an "Alice In Wonderland" themed tea party, jurors heard.
Over the next three days, Rizlaine and her mother Mina Dich, 43, carried out reconnaissance around major landmarks in Westminster and bought a pack of knives and a rucksack, the court heard.
But on April 27 last year - the day of the proposed knife attack around the Palace of Westminster - police swooped to arrest Rizlaine Boular, jurors were told.
Rizlaine Boular, of Clerkenwell, central London, has already admitted planning an attack and with the help and support of Dich, the jury was told.
But Safaa Boular, now 18, who lived at home with her mother in Vauxhall, south west London, has denied two counts of preparing acts of terrorism.
Opening the Old Bailey trial, prosecutor Duncan Atkinson QC told jurors Safaa Boular planned to "unleash violence and terror in the heart of London".
He said she was inspired following a failed bid to marry IS fighter Hussain, who was in his 30s.
After just three months chatting on social media, the couple had declared their love for each other, the court heard.
Safaa Boular wanted to marry Hussain and don a suicide belt each, jurors were told.
Mr Atkinson said: "Their plan then was that together they would, as Hussain put it, depart the world holding hands and taking others with them in an act of terrorism."
But Boular's aim to travel to Syria accompanied by her sister was scuppered when she was stopped by police at Stansted en route home from a holiday in Morocco in August 2016.
Boular allegedly switched her attention to Britain, keeping contact with Hussain on a secret phone through encrypted Telegram chat.
But British Security Services had deployed specially trained role play officers to engage with the pair online to keep track of their activities.
Both Hussain and Boular talked about an ambush involving Russian-style guns and "pineapples" - code for grenades, jurors heard.
The defendant sobbed when she found out about Hussain's death in April last year, and was comforted by her sister and mother, who told her "he's in paradise".
She told an officer posing as an IS fighter that all she needed was a "car and a knife to get what I want to achieve", the court heard.
She allegedly confided that she had no time to "lounge around", adding: "My heart yearns to be reunited with my dear husband for the very first time."
In encrypted chat, she said Hussain had told her "something about a British Museum and the tokarev and pineapple", Mr Atkinson said.
Tokarev was said to be a type of Russian gun and pineapple, a code word for grenades.
In a conversation on April 8 last year, Rizlaine Boular allegedly told her: "The bus goes past the British Museum and I thought of you", in apparent reference to the target.
But on April 12, Safaa Boular was charged with planning to go to Syria so was unable to carry out her "chilling intentions", Mr Atkinson said.
Instead, she encouraged Rizlaine "to carry the torch forward in her stead" in telephone calls from prison, he said.
Joel Bennathan QC told jurors that Safaa was "groomed" by Hussain, who was twice her age.
In an opening speech, he said: "She was a child who was sexually groomed, someone who was groomed to be radicalised. That's what happened to this young person."
He added that her family had "encouraged" and "celebrated" it.