The sister of a woman who was murdered 42 years ago along with her young son, has made an emotional appeal for information in the unsolved case.
Renee, 36, and three-year-old Andrew MacRae disappeared on 12 November 1976.
Mrs MacRae's car was found later that same day on fire in a lay-by on the A9 south of Inverness.
Her sister, Morag Govans, said: "Even after the passage of time I believe that there are people who know what happened to Renee and Andrew."
She added: "I will never give up hope of getting justice for them both."
Police Scotland has also renewed its appeal for information.
Its new plea includes a request for the author of an anonymous letter sent to police in 1982 to get in touch.
Posted to Northern Constabulary, the letter included details of activity at an unnamed quarry on 12 November 1976.
Two quarries in the Highlands have been searched on various occasions as part of the police investigation. Dalmagarry Quarry is close to where Mrs MacRae's BMW was found, while Leanach Quarry is at Culloden Moor near Inverness.
On the evening of her disappearance Mrs MacRae, who was estranged from her husband Gordon, had set off with her youngest of her two sons, Andrew, to meet her lover Bill McDowell, Mr MacRae's married accountant. He told police they never met.
'Life cruelly ended'
Making her appeal for information, Ms Govans said: "More than four decades on the pain of losing Renee and Andrew doesn't ease. Not a day goes past that both are not in my thoughts.
"Andrew was just three-years-old, a mischievous and fun loving wee boy. It is impossible to take in that his life was brought so cruelly to an end at such a young age.
"He would have turned 45 in October and I often wonder what he would have been doing now with the life that he was never given the chance to build.
"Renee was a compassionate and caring mother. Both Andrew and his elder brother Gordon were her life. She adored them and was so proud of her boys.
"Gordon was only eight and has lost the love and guidance of his mum and brother."
She added: "I appeal for anyone with any information to come forward and for others to examine their conscience to end 42 years of pain and anguish to allow us to grieve for Renee and Andrew."
Det Insp Brian Geddes said modern policing techniques, including forensic science, were being applied to the unsolved murders.
He said Police Scotland's Major Investigations Team was "pouring through every single item" the force held on the case in a bid to identify new lines of inquiry and develop any existing lines of inquiry.
The officer said: "All the indications are that Renee and Andrew came to harm 42 years ago and as such this is being progressed as a murder investigation.
"The initial investigation and the various reviews and re-investigations since 1976 appear to have been very thorough and have generated a great deal of material."
Renee and Andrew MacRae: Timeline
17:00, 12 November 1976: After dropping off her eldest son, Gordon, at Mr MacRae's home, Mrs MacRae and Andrew leave Inverness for Perth.
22:00, 12 November 1976: Mrs MacRae's BMW car is found on fire by a passing bus driver about 12 miles (19km) south of Inverness. The car is parked on a loop road that was being used as a lay-by during the construction of then new A9 trunk road. Blood is found in the boot of the car. But there is no sign of the mother and son and police begin what would become one of the UK's longest missing persons investigations.
1976: In the fortnight following 12 November, more than 100 police officers and large numbers of volunteers search moorland around the site of where the car was discovered. RAF Canberra aircraft make wider sweeps of the area.
1977: Divers search flooded Leanach Quarry, a known fly-tipping spot, near Inverness.
August 2004: Police return to Dalmagarry Quarry, which was searched at the time of the mother and son's disappearance. Northern Constabulary drafts in internationally experienced forensic archaeologists and anthropologists to sift 35,000 tonnes of soil from the disused quarry, near the lay-by where Mrs MacRae's car was discovered, but no sign of the mother and son is found. New tests are also carried out in a laboratory in Aberdeen on traces of blood found in the boot of the BMW.
2016: A report naming a suspect who may have killed the pair is sent by Northern Constabulary to prosecutors but they decide there is insufficient evidence to take action.
October 2018: For about a week, Police Scotland divers examine Leanach Quarry using a remotely operated vehicle.
9 October: To mark Andrew's 45th birthday, police release a photograph of him and an image of the Silver Cross pram owned by his mother. Officers appeal for sightings of the pram on and around 12 November 1976.
Det Insp Brian Geddes added: "Our goals are to bring a person, or persons, to justice and to locate the remains of Renee and Andrew in order to bring some form of closure to Morag and the rest of the family.
"We will draw on the investigative expertise from within our organisation and beyond, and I have assured Morag and her family that everyone involved in the investigation is fully committed and will leave no stone unturned in a bid to find the answers the family deserve."
Det Insp Geddes said the person or persons responsible for the murders were likely to "have enjoyed a life", adding that this was something denied to the mother and her son.
He went on: "With that in mind I would again appeal to anyone who has information, even if they are not sure if it is important, to come forward and contact us.
"Specifically, I want to take this opportunity to appeal to someone who wrote anonymously to Northern Constabulary in 1982 regarding information surrounding activity at an unnamed quarry on 12 November 1976.
"It appears that this person had moved away from the area in the subsequent years. If you recognise yourself as the writer of this letter then I urge you to get in touch with the investigation team."
Clues from the past?
Witnesses in 1976 told of police of seeing someone dragging a sheep near the A9 - Mrs MacRae was wearing a sheepskin coat the day she disappear - while another witness said they saw a man with a pushchair.
During the early days of the investigation, a police sergeant and a digger driver described encountering a strong smell during an examination of Dalmagarry Quarry.
Police returned to the quarry in 2004.
Over a period of three weeks, tonnes of earth and 2,000 trees were excavated and removed at a cost of more than £100,000. Nothing but crisp packets, some men's clothing and animal bones were reportedly found.
Det Insp Geddes said the passing of 42 years was "undeniably a long time", but was not a barrier to justice.
He added: "Someone out there knows what happens to Renee and Andrew and I hope this appeal today serves as a reminder that it is never too late to come forward with information."
"Anyone who believes they can assist Police is asked to contact 101 or you can e-mail a dedicated inbox at SCDHOLMESInverness@scotland.pnn.police.uk."