Derek lived on the banks of a lake that was home to a monster. This creature only emerged from the water at night. Sightings were rare, but people for miles around could hear his roar every time he rose above the surface of the lake.
Derek believed that the monster was lonely, and that all he needed was female company. No one in the area knew how to determine the gender of underwater monsters, but it was widely believed that this one was male because experience had taught people that only men roar in the middle of the night and wake up the neighbours. Experience had taught Derek that these roars were often inspired by female company, or the lack of it. Of course, alcohol almost always played a part as well, but this was hardly likely to be a factor in the monster's expressions of despair. It was difficult to imagine a greater commitment to teetotalism than living in water.
Derek wanted to help the creature in the lake. At times it was heart-breaking to hear the monster's plaintive cry, evoking a sense of a lonely existence, but most of the time it was just annoying to be woken in the middle of the night. Derek wanted to find someone who could give him an insight into the psychology of the monster. He asked the neighbours if they knew anyone who could help. No one knew of a monster psychologist, but Mrs. Thomas did have a brother who studied child psychology. Derek didn't think that Mrs. Thomas's brother would be able to offer much help in this instance, so he tried asking the people whose lives were full of strange phenomena, the men and women who roamed the land at night to meet fairies and the spirits who were permanently lost in the hills, like the ghost of the hiker who'd been wandering around for centuries, constantly thinking about the sausages he'd left on the frying pan back at his camp site. For these people there was nothing strange about encounters with ghosts, and for some of them there was nothing strange about constantly thinking of sausages, but none of them had any experience of lovelorn monsters.
As a last resort, Derek tried looking in the phone book. He was amazed to find an ad for a service that dealt with monsters of all shapes and sizes, from the smallest ones who set up horrid homes in handbags, to the enormous monsters who live in lakes or dance in the sky, generating their own clouds to disguise themselves (it's easy to see through the disguise when you see two clouds dancing). The ad promised an expert insight into the psychology of monsters. Derek was delighted when he read this. It meant he wouldn't have to contact Mrs. Thomas's brother, and he was glad because he'd heard that Mrs. Thomas's brother was just like Mrs. Thomas.
The service was provided by middle-aged twin sisters. When they arrived at Derek's house they had suitcases with them. They told him they'd need to stay overnight to hear the monster. Derek had a feeling that this abundance of female company would turn out to be worse than not having any, but he was encouraged by the antipathy they showed for his company. They rarely spoke to him, and they insisted that he call both of them 'Miss Watson'. This suited Derek because he would have found it difficult to tell which one was which if he'd known their names. He appreciated their silence as well because he got the impression that they'd complain about his house if they were more willing to talk to him.
Derek was woken in the middle of the night by the sound of the monster's roar, and on this occasion he welcomed the noise because Miss Watson would hear it as well, and hopefully it would offer them some insight into the monster's problems.
In the morning they told him that the monster was actually female, and her biggest problem was that her wings weren't working. She used to be able to fly, but she'd been confined to the lake for the past fifty years. Miss Watson suspected that a magic spell was the source of the wings' malfunction. They said they might be able to reverse the spell, but they'd need to listen to the monster's roar again to find out more. Derek was relieved to hear there was a chance he'd get a good night's sleep some time in the near future, and he told Miss Watson they could stay with him for as long as they wanted.
When they were still staying in his house three weeks later he started to wonder if he'd be better off with sleepless nights. He didn't know if they were making any progress with the spell because they were so reluctant to talk to him. And then Henry, one of the people who seek strange phenomena, came to see him to deliver a message that had been passed on in a dream. In Henry's dream he'd been told that the twins weren't really monster psychologists. Sometimes they posed as ghost-catchers and sometimes as mediums. The purpose of all their roles was to find a place to live. Their job would supposedly require an overnight stay, but they could be there for months. They'd been homeless for seven years, ever since losing their house after losing most of their money in a bad investment.
Henry's message seemed believable to Derek, though he was reluctant to trust a man who devoted most of his spare time to his attempt to make paperclips out of butterflies, an obsession that began with an interest in alchemy. After another week of the twins' company, Derek decided it was time to tell them that he no longer required their services. Learning to live with the monster seemed easier than learning to live with two women who'd happily spend an evening silently expressing their antipathy for him and all he stood for, radiating their contempt around the house. When Miss Watson was standing at the edge of the lake one day he went to see them to inform them of his decision. He'd practised this speech in advance, but he didn't get far into it when he was interrupted by the monster, who emerged from the water and kept rising upwards, carried away by her wings. She let out one final roar before she departed, and Derek suspected that this one could be translated as 'thank you'. He watched in awe until she disappeared from view. He was speechless, but he did his best to make a noise that could be translated as 'thank you'. The twins remained silent. Miss Watson gave him their bill. When he saw how much they were charging he made a noise that would have to be bleeped out if it could be translated into English. He couldn't possibly afford to pay them what they were asking, but he saw another way of settling his debt. He offered them free accommodation instead of money. They accepted his offer, and he detected faint smiles on their faces. He took this as a sign that they'd turn out to be easier to live with than the monster.