When Katherine Parker-Brice's new next door neighbour spotted a cat she believed to be a stray in her garden, she called the RSPCA.
It sent out an inspector who agreed with her assessment - and swiftly killed the animal by lethal injection.
But both got it horribly wrong...the cat was Mork, one of two tabbies loved and cared for by Katherine and husband Paul for 19 years.
Now the furious couple are taking legal action against the RSPCA after the inspector killed their healthy pet - and added insult to injury by returning it the next day in a plastic bag.
"I had only been out of the house a few hours but in that time he collected Mork, drove him around in a cage in the back of his van and then killed him, inexplicably, in his front garden," explained Mrs Parker-Brice.
"This man's broken our hearts. He has left Mork's sister, Mindy, without a companion. They were together for 19 years and have now been torn apart by a careless, casual act. The RSPCA quickly prosecutes anyone who neglects animals - yet here it is killing them indiscriminately."
Mrs Parker-Brice, 45, from Ruislip, Middlesex, told how her next-door neighbour, who was new to the area, had contacted the charity as the cat climbed into her garden.
But instead of leafletting neighbours or putting up posters to establish ownership or taking it to a vet - all normal RSPCA procedure - the inspector drove the cat off in his van.
And just two-and-a-half hours after collecting the animal, he killed it outside his home.
Mrs Parker Brice said: "I had arrived home from work that day at 4pm and was calling out for Mork but he wasn't around.
"He is an indoors cat, very loving and playful, but gets distressed if he goes too far from home. We found out from the neighbour that she had called the RSPCA but it wasn't until late at night we tracked down the inspector.
"I was in tears. He tried to defend himself saying the cat didn't have any teeth and was old but it was ridiculous. You only had to look at his nails which had been clipped and his glossy coat to see that he wasn't a stray. We demanded he bring the cat back, which he did the next morning, but he put him in a yellow plastic disposable bag."
The inspector, who had been with the RSPCA for ten years, faced a disciplinary hearing but received only a written warning.
"He should have been sacked - there is no way he should be allowed near animals," said Mrs Parker-Brice, a driver for the RAF.
She said her seven-year-old daughter, Samantha, who wants to be a vet, has ripped the RSPCA stickers off her collection of Animal Hospital toys because she was so upset.
Mrs Parker-Brice said: "What I can't help thinking about is the period leading up to Mork being killed. He would have been alone in the dark in the back of that van for two hours and it would have terrified him. He has never been alone before.
"His sister is pining for him. She keeps wandering around the house looking for him."
The RSPCA admitted that the inspector had followed none of the RSPCA's normal procedures.
In a statement the charity It said: "The RSPCA said: "We would like to offer our most sincere and heartfelt apologies to this family, who have lost their pet cat Morky.
"In this instance, an RSPCA animal collection officer tried to do the right thing but made a tragic mistake.
"We would point out that the ACO had the best intentions at heart when dealing with Morky. He believed the cat to be stray, extremely old, ill and suffering.
"As a result he took the decision to euthanase the cat as soon as possible to put an end to the suffering he believed it to be experiencing.
"Following a lengthy investigation the ACO was brought before a disciplinary hearing and action has been taken. The individual has been disciplined and re-training is also being provided.
"The superintendant of the region has personally visited the family to offer his most sincere apologies. The ACO - who has 10 years of experience with the RSPCA - feels great remorse over this tragic mistake."