Page 29 of The Secret Christmas Library

But when she looked at the walls she realised they were smooth: no doors anywhere, and the windows were fewer and further apart.

Mirren frowned to herself. Well, it had to come out somewhere; this was ridiculous.

There must be a fire exit. Even as she thought this, she figured that, actually, this building rather pre-dated the existence of fire exits.

Curiously, she carried on, down and down. It became darker, and colder, but if she peered she could see a light below her. Perhaps she was right at the back of the house, and it went down. She’d probably find herself by the bins.

She touched the walls to steady herself in the gloom. They were damp, and something slimy touched her fingers. She shuddered and rubbed them on her jeans. ‘Ugh, bloody hell.’

But the idea of climbing all the way up hundreds of steps again didn’t appeal either, so she carried on down. The white circle of light grew larger; but it looked strange, bobbing in front of her eyes. She blinked, in case it was her eyesight, but no, something was definitely moving . . .

Near the bottom the steps were all wet, and dangerously slippery, and she finally realised – feeling quite the idiot as she did so, considering their geography – exactly where she was.

Sure enough, the steps coiled round a few more times, slippery with seaweed, and deposited her in the corner of a dark cave, the wobbling light being, of course, the shallow waves running up the shingle.

She had come right out through the castle to the beach beyond; she had gone all the way down the cliffs, through a secret passageway that led here.

‘Bloody hell!’ said Mirren, firstly to herself, then out loud. The noise echoed off the close walls of the cave. ‘Hello? Hello . . . hello?’

There was no answer. She glanced over. The opening to the cave was small; it must be imperceptible from the other side. A secret escape route! It was rather thrilling. No wonder there weren’t any more doors leading on to it.

Her eyes adjusted to the dimness, and, looking round, she saw, pulled up on the shingle, an old rowing boat, decayed and covered in barnacles.

Goodness. She wondered if anyone ever came down here, or even knew it was still here.

Well, they must do. She glanced at her feet.

The waves were coming up to her toes. She supposed the tide must fill this place – that was an unpleasant thought.

She glanced up just in case there were any rings drilled into the wall to chain unfortunates, but didn’t see anything like that.

But in doing so she leaned out, took two steps – and the door, which had been propped open, swung closed behind her.

Mirren let out a cry of dismay as the door slammed shut.

It was completely smooth; the same colour as the rock – if you didn’t know it was there, you would hardly be able to see it, tucked away behind a pile of rocks at the far back of a cave.

Which of course was how it was designed, but her fingernails on the door didn’t make the slightest bit of difference; there was no clawing it open.

‘Oh, bollocks,’ she said, glancing at the tide.

She was right: it was definitely coming in, washing further up than it had before.

And she had no idea how deep this cave was.

She might come out into full North Sea. In December.

She could die. She was suddenly furious with Jamie and Esme for not warning her about this.

It was so dangerous! What the hell were they thinking?

She was freezing now, and genuinely frightened, as well as feeling absolutely ridiculous – two days ago she had been cheery because she’d just got the last stamp on her coffee loyalty card, for goodness’ sake, and now she appeared to be in danger of losing her life in a bloody cave in Scotland.

Her body would probably wash out to sea and she’d never be heard of again.

And then Theo would be sorry he ghosted her, she thought, darkly.

She tiptoed, gingerly, to the mouth of the cave, the wind blowing fiercely outside. The waves were a steely grey.

She noticed, on the right-hand side, a slightly higher, climbable rock, and, splashing across the shingle, hauled herself up on it.

From there, she could work her frozen fingers round the mouth of the cave, and she found, to her surprise, delight and slight embarrassment, some cold grass – grass did not, of course, grow underwater.

She must have reached the limits of the high tide, only a couple of feet above the floor of the cave.

There was another stone laid there, like a small stairway, and she heaved herself out on to that and found another one, and then another; casually laid, so they didn’t look deliberate, just like random stones, but she was pretty sure they were there on purpose – and, with some effort, she managed to pull herself finally on to the little snowy outcrop of land.

Feeling rather foolish, she turned a hundred and eighty degrees and realised exactly what she was looking at.

The sheer cliff ran straight up from the sea – when she had looked down from the drawing room side window, this was what she had seen.

The castle, so formal from the front, from the back looked completely organic, as if it had grown out of the very stuff of the rock itself, a natural part of the crags.

This must be the oldest section. The cave was well hidden at the bottom by this promontory of grass, presumably, underneath the snow; another one curved round the other side, forming a minuscule natural harbour.

Brave would be the marauders who attempted to attack from the bottom, but you could nudge the boat out from the cave with complete and utter privacy and go – well, anywhere, she supposed.

She was truly cold now, and her wet feet were rapidly numbing.

Her heart sank as she looked up the crag, but there was nothing else for it: she had to scramble her way up through the snow in an unusually undignified fashion.

She found herself using muscles she hadn’t for years; at one point she pitched forward headfirst and went knee-deep in the snow.

The ice scratched her face, and she was so annoyed with herself that she swore.

After what felt like an age, she finally made it to the foot of the castle, and headed round the back first, which for once turned out to be the right decision, as she soon found the kitchen garden and, from there, the kitchen door.

She could even hear the chatter. The snow had been crudely pushed away from it, with a spade in the corner; footprints – human, dog and bird – criss-crossed the area in between the door and the kitchen garden and beyond.

With a sigh of incredible relief, she pulled open the door and fell into the blessedly warm kitchen. Whereupon she was greeted with, first, total silence, and then, swirling up, a great roar of laughter.