The heartbroken parents of missing Nicola Bulley fear "somebody got to her" after saying she was in "good spirits" when they last spoke with her.
In their final conversation before her disappearance, Nicola's parents, Ernest, 73, and Dot, 72, said her "mind was great".
The couple vowed they "will never stop looking for her" as the operation to find Nicola enters its sixth day.
Speaking to the Mirror, they said the disappearance of the 45-year-old mum from in Inskip, Lancashire, was totally out of character.
Ernest said she had no health problems and was in good spirits enjoying her job.
He added: "Her mind was great, we picked the children up the Thursday before she went missing, as we do every Thursday.
"We took them home, Nicola had had a meeting with her boss in Garstang and she said can you stay a bit later because I have an important client coming in on Zoom. We said 'no problem' and stayed.
"She had done her work and she was very upbeat about getting her mortgage sorted.
"I said we better go now and Nicola came to the front door, and I gave her a kiss and told her I loved her and that was the last conversation I had with her."
Nicola dropped her young daughters at school and left the car parked up in St Michael's village and was last seen walking her dog on a footpath along the River Wyre at around 9.20am on Friday before she vanished.
A major search involving drones, sniffer dogs, specialist divers and a police helicopter has been unable to turn up any more clues, leaving her parents fearing the worst, especially with no evidence of Nicola having fallen into the river.
Ernest said: "There was no sign of a slip or falling in so our thought was 'has somebody got her'?
"I asked the Sergeant from Fleetwood a few days ago, 'is there any chance of her being taken' and she said 'I don't think that's the case'.
"I said 'how can you know that?', it's such an isolated area, the only way that has happened is if it was someone who knew her."
While Nicola's family live in hope of her turning up, Ernest confessed their worst fears: "We just dread to think we will never see her again, if the worst came to the worst and she was never found, how will we deal with that for the rest of our lives."
But Ernest vowed: "We will never stop looking.
The couple who are joint owners of a freight transport company have split their time between caring for their grandchildren, Nicola's two young daughters, and looking for their own daughter.
Just over an hour after Nicola's last confirmed sighting, a member of the public raised the alarm with police when they found Nicola's dog Willow running loose by the river.
Police arrived at the scene and found Nicola's phone on a bench, still connected to a work conference call.
They began searching for Nicola, a mortgage advisor, immediately.
But since then her family have endured an excruciating wait for answers.
For mum, Dot, the nights are the hardest.
She said: "Our worst time is when it gets dark.
"We find it really hard to think about wondering 'is she ok' and 'where is she?'
"But [the police] tell us 24 hours a day they are on it and still working.
"You wake in the night and you can't get back off to sleep."
On Monday, Nicola's long-term partner Paul Ansell, 44, described the situation as "perpetual hell".
But on that same day, grandad Ernest described his heartbreak at hearing the girls "sobbing their hearts out" when they were told "mummy is lost".
He added: "We don't know how long we can keep going before they realise, they think mummy is coming home soon, but if this keeps going on and on I don't know where we are going to go or what to say to them."
All members of the family have been involved in the search for Nicola in some way, particularly her younger sister, Louise, who has been out every day according to her parents.
The sisters had been excitedly planning a spa break the night before Nicola vanished.
Dot said: "Louise had just booked Ribby Hall because they both had spa vouchers, she had just sent Nicola the night before the treatments.
"Louise booked it on Friday morning and sent it to Nicola but she never got back to her. "They are very close."
Nicola who "lived for her children" had also bought tickets to watch them perform at choir and gymnastics shows in recent weeks.
The family applauded the efforts of Lancashire Police as "marvellous" but are just desperate for clues to beloved Nikki's whereabouts.
Lancashire Police are keeping an 'open mind' but said they do not believe Nicola has been attacked.
Ernest said: "I think the police thought initially when they saw the phone on the bench and the dog wasn't tethered that she may have gone into the river and that was their main line of search."
It was the lack of any evidence of Nicola having suffered a slip or falling into the water that led the parents to consider someone else may have brought harm to their daughter.
Either way, their hope is that with all the media surrounding Nicola's case, someone will spot her and report a sighting.
Ernest said: "There's so much coverage, it's like a manhunt and at this moment in time we're still no further down the line there's still no clues.
"If we found a part of clothing, a scarf, anything that was found somewhere then there would be a different line of enquiry but there isn't.
"We have found nothing. Louise asked the police the other day, when do you stop looking and he said 'we don't, we keep going until we find somebody'."
Anybody who has seen Nicola, or has information about where she might be, is asked to call 101, quoting log 565 of January 30th. For immediate sightings please call 999.
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