Four siblings died from smoke inhalation after a teenager deliberately started a fire in a bedroom wardrobe, a jury has heard.
Four-year-old twins Holly and Ella Smith and their two-year-old brother Jordan were asleep as the blaze took hold while elder brother Reece, 19, was overcome by fumes as he went upstairs to try to rescue them.
The teenager accused of their murders, Dyson Allen, 19, was the only other person who was upstairs at the dormer bungalow in Freckleton, Lancashire, when the fire broke out, Preston Crown Court was told.
A birthday party was being held for the children's mother, Michelle Smith, at the address on the night of the fire on January 7 last year.
Neil Flewitt QC, prosecuting, said: "It is the prosecution's case that the defendant, Dyson Allen, was responsible for starting that fire and he did so deliberately."
The fatal fire began inside a wardrobe in the bedroom shared by the three young children and their mother, said the prosecutor.
Three family friends were also in the house along with the defendant who was a friend of another of Ms Smith's sons.
Allen was a regular visitor and stayed overnight the evening before the blaze, the jury was told.
He spent most of the night on January 7 in the second upstairs bedroom, according to those who were in the house, said Mr Flewitt.
He continued: "Michelle Smith had allowed Dyson Allen to store some of his personal belongings that were in a large blue Ikea bag in bedroom one (the young children's room).
"The presence of that bag may be significant because it would provide a reason for Dyson Allen to go into that bedroom.
"Apart from the three young children who were asleep in their beds, he was the only person upstairs when the fire started and he was the person that alerted the other occupants of the house to what was happening."
Mother-of-nine Ms Smith, 37, said she said remembered the lights going off and then the defendant jumped down the stairs and shouted "Fire" before he ran through the kitchen and out of the back door.
Mr Flewitt said: "Michelle Smith's memory of subsequent events is understandably not clear but she recalls being taken out of the house and sitting on the little wall at the end of the driveway.
"She doesn't remember Reece going up the stairs but she remembers him being brought out and everyone gathering around him.
"Thereafter she was taken in a police car to the hospital where she discovered that four of her children had died in the fire."
Ms Smith told police that smoke alarms had been fitted at the top and bottom of the stairs but Reece had taken them down in the days before the fire because one or both of them kept making beeping noises.
She said she took the twins up to bed at about 10pm to join Jordan who was already asleep.
The prosecutor said: "She is sure that the doors to the wardrobe were closed when she left the room because it annoys her if they are left open so she always checks that they are closed and that the children's dressing gowns are hanging from the handles."
Allen, from the Freckleton area, denies four counts of murder and four alternative counts of manslaughter.
The court heard the recollection of most of the witnesses who attended the party was "affected to some extent by drink and in some cases by drugs in the form of cannabis."
Mr Flewitt said: "In particular, most of the witnesses are unable to say with any certainty at what time various events occurred."
It could be established though that the first 999 call to report a fire was made at 11.20pm by a neighbour.
And that some time after 10.45pm one of the family friends, who was sober, went up to the bedroom where Allen was.
He said the defendant appeared "drunk and stoned" after Allen had earlier told him was going to make a mix for a cannabis bong.
When he returned downstairs there was a loud bang shortly after and all the lights in the house went off.
In a witness statement given to police in the early hours of January 8, Allen confirmed he was a friend of Reece and one of the victim's younger brothers.
He said he began celebrating Ms Smith's birthday at lunchtime by drinking from a bottle of vodka.
Allen said he was upstairs when the lights suddenly went out and he thought it was a power cut.
He saw the children's bedroom door was shut but he could see an "orange glow" in a gap at the bottom.
"I opened the door to check and all of a sudden thick black smoke just hit me in the face," he said.
"It knocked me backwards.
"I started shouting 'fire, fire' straight away."
He said he told Reece there was a fire and to "get those kids out".
He ran downstairs to rouse a person who had fallen asleep on the sofa and then ran outside.
The court heard that Reece was heard kicking at the door to the children's bedroom as others escaped from the property.