It was midnight and British nurse Janny Dearing was asleep when she heard what sounded like "artillery fire" outside her window.
This was probably grenades being launched at the security checkpoint at the entrance to the Muhaya compound.
Minutes later the massive car bomb was detonated.
"We didn't know what was happening. We looked out of the window and realised it was gunfire," she said.
At least 17 people died in the Riyadh bombing
"We crawled along the corridor to get the kids. Screaming, smoke, we just got under the beds and then there was the explosion. Terrifying."
Mrs Dearing and her Canadian husband both work at Riyadh Military Hospital.
They have two children, Robin, aged 13, and Scott, 11.
"They were very scared, trembling during the gunfire. They knew their lives were in jeopardy," she said.
"We didn't know if someone was going to come round and shoot us. There will be after effects."
The rubble has now been bull-dozed away at the site of the blast.
The crater left by the massive car bomb - five metres (16 feet) across and three metres deep - has been filled in.
The area is still sealed off. Dozens of Saudi Interior Ministry special police are milling around.
A jeep with a heavy machine gun stands guard outside.
Residents of the compound are seen carrying away their belongings in carrier bags - even those buildings not destroyed are too badly damaged to live in.
Every pane of glass is shattered.
The compound's roads are full of cars shredded by shrapnel.
The reaction of most Saudis to this attack has been angry and emotional - especially as the bombing killed Arabs and Muslims.
And during Ramadan.
This mood is reflected in the newspaper coverage.
The Saudi Government has vowed to crush the militants
The front page of the main broadsheet el-Watan has pictures of dead and injured children.
Graphic colour shots of the casualties dot the rest of the paper.
There is a story about a pregnant woman impaled on an iron bar by the force of the blast.
The broadsheet al-Jazeera has a whole double page spread just filled with condemnations from ordinary citizens.
"We ask God to destroy those criminals who do not respect Ramadan," says one typical remark.
"We will confront terrorists with an iron hand," the country's ruler, King Fahd, told the weekly cabinet meeting.
The king is elderly, and thought to be infirm.
He is rarely seen but this his appearance at the cabinet meeting led the news on state TV and was on most of the front pages.
'Actions against Islam'
"The royal family is both livid and nervous," was the assessment of one senior western diplomat.
What, perhaps, makes the Saudi establishment most nervous of all is the attempt by al-Qaeda to exploit the piety of most Saudis and portray themselves and the true guardians of Islam.
So the country's top Islamic cleric here, Sheikh Saleh al-Sheikh, also the minister of Islamic affairs, has issued guidance in the wake of the bombing.
"The devil shouldn't drag us to sympathise with those who speak in the name of Islam but whose actions are against Islam," he said.
Call for reform
The billionaire investor, Prince al-Waleed ibn Talal, told Saudis on Monday to abandon "stupid conspiracy theories" which blamed foreign hands for every bad event in the kingdom.
This was not the work of the Mossad or the CIA, he said.
Prince Waleed also said that the kingdom had yet to ask itself honestly why 15 or the 19 hijackers on 11 September 2001, were Saudis.
He called for political reform to root out extremism.
Above all, he said, there should be full democratic elections.
"Reform is not a requirement of businessmen only or members of the ruling family but a requirement of every Saudi citizen," he said.
The Saudi royal family do not believe they can buy off al-Qaeda with political reform.
Reform is aimed at winning the hearts and minds of their own people - to ensure their loyalty in a struggle which ultimately is about the survival of the ruling family in power.
So whatever happens in the battle against al-Qaeda, no-one doubts that the next 12 months will be a time of immense change in Saudi Arabia.