It’s twilight, the sky darkening to indigo when Sarah storms out of the house. Her rage and frustration at boiling point, she fails to see the small figure in a goblin mask standing at the foot of the three steps. She doesn’t register the oddly deep voice in which it says, “Trick or treat, lady.” Nor does she realise that her heavy bag, swinging from her shoulder, sends the small goblin sprawling in the mud.

Shoulders hunched, hands thrust deep into the pockets of her duffel coat, Sarah crosses the road and enters the park, kicking furiously at the autumn leaves.

Bloody Luke. He knows how much she wants a child and, at one time, so did he. But now, with her fortieth birthday only a few weeks away, he’d said flatly that there would be no more IVF, they’d spent enough money and, quite frankly, he didn’t want to be a geriatric father.

Sarah walks until she’s exhausted, fighting back tears, knowing there’s no way Luke will change his mind. At last, she sits down on a bench to calm herself before returning home. It’s full dark now and there are few people left in the park, only an odd family group, kids dressed as ghosts and princesses clutching bags of sugar-laden treats. Sarah groans. Of course, it’s Hallowe’en. Hopefully, Luke has handed out the treats she left in the hallway.

A solitary figure appears on the path a little way to her left, a small child wearing a goblin mask. Sarah starts rummaging in her bag, hoping to find a chocolate bar to give the child. When she looks up again, standing before her is a little girl about three years old, her long dark hair tied back with a green ribbon.

Sarah looks around for the child’s parents, but sees no one. Rising, she kneels in front of the little girl and says, “You poor thing, you must be frozen.Where’s your mummy, sweetheart?”

“Mama?” says the child questioningly.

“Yes,” Sarah answers, thinking perhaps the little girl is foreign. “Mama.”

The child smiles, her lips stretching wider and wider revealing sharp yellow teeth. Sarah falls back, stretching out a hand to save herself, wincing as a splinter from the bench drives into her hand. A strangled scream escapes her as, terror-stricken she bolts upright, looking wildly around the dark, empty park. The child – the goblin? – is gone. She closes her eyes, presses fingers to her temples. Had she dozed off in spite of the cold, dreamt of the child she so badly wanted?

“Yes, just a bad dream,” she whispers and, trying to erase the image of the little girl’s ravaged face from her mind, she sets off towards home. Luke will be wondering where she is.

To her doctor’s amazement, Sarah falls pregnant and gives birth to a baby girl in late July. An ugly baby girl with a wide mouth and drooping eyes. As the weeks pass, however, the little face fills out, the eyes round and blue and the mouth as pretty as a rosebud. Sarah adores the child, who she names Joy, and Luke tries not to show that she gives him the creeps.

That year, it rains on Hallowe’en and the streets are quiet. Sarah answers the door as dusk falls to find the goblin creature standing at the foot of the steps. Bowl of treats slips from her nerveless fingers and she sits down heavily on the uppermost doorstep,

“No,” she croaks brokenly, “please don’t take her.”

For Sarah knows now that she has a goblin girl. When Joy is in distress or in need of care, her mouth will widen slightly and her eyes begin to droop. Always, Sarah will rush to placate the child, breathing a sigh of relief when the little face returns to normal. So far, she has managed to keep Joy’s true nature from Luke. And she’ll do anything to keep her.

“Trick or treat, lady,” says the goblin, holding out a claylike hand.

“Yes, yes,” she gasps, scrabbling to pick up the chocolate bars, freezing when a long fingernail touches her neck, followed by a tug at her earring.

“Gold,” the creature says.

Sarah rips the jewellery from her ears and thrusts them into the outstretched hand, falling to her knees in the mud. “And you won’t take her?” she begs.

“Not this year, lady.”

And so, Sarah pays the goblin every Hallowe’en, fearful of what will happen when she has no jewellery left or enough money to satisfy the avaricious creature.

In the year when Joy turns three, Sarah spends the afternoon of Hallowe’en in town with Luke, finalising their divorce agreement. The meeting takes longer than expected and she barely has time to get home before the dreaded knock on the door. Taking a bend too fast, she crosses the white line and scrapes the side of a car coming the other way. She brakes to a halt, leans her head on the steering wheel and weeps. All hope is lost.

The front door is wide open when Sarah reaches home, the house deserted, Joy and the babysitter gone. And she runs. Across the road and into into the park, through trees with an early mist clinging to their branches, trampling over dying flower beds, fighting for breath, her heart pounding in her chest, soundlessly sobbing Joy’s name. At last, exhausted, she sinks to the ground, head dropping defeated.

From somewhere nearby, a woman says, “What are you doing out here on your own, poppet? Where’s your mummy?”

And a heartbeat later. “Mama?”

“No!” Sarah screams, lurching to her feet, running frantically towards the voices. “No! She’s mine! Joy!”

Now she’s on a path she recognises. Her heart leaps. Is that a young woman, kneeling and talking to a little girl? She runs even faster, her breath ragged, mist swirling around her in the darkened park. Now she can only see the small figure.

“Joy,” she sobs. “It’s me, Mummy.”

The goblin turns, grins widely.

“Trick or treat, lady.”