Two prompts combined in this one! I've put them at the end to avoid spoilers.

For many years, my readers have clamoured for the unfortunate story of the Dutch steamship Friesland. Hopefully they will not take amiss that the adventure I am about to recount, despite its connection with a boat, is not that horrifying tale. The world is not yet prepared for such a shock, although this story also contains some elements that may shock and horrify the more sensitive reader.

It was in the year 1902 that Captain John Gruen (Ret'd) first arrived on our doorstep, with the proud bearing and ruddy complexion of a naval officer of many years standing. "Mr Holmes," he said stolidly, gaze flickering between my companion and myself before settling on the former, "I have come a long way to consult with you."

Holmes, languidly sprawled in his armchair, waved a pale hand towards the lounge. "Please, take a seat. After your early start, and your little scuffle on the street on your way here, I'm sure you could use one."

Gruen looked startled. "I've heard of your powers, Mr Holmes, but how could you know about the thief? Not even the police know yet."

"I have my ways." He smiled.

My long acquaintance with Holmes' methods allowed me to see the hasty shave and slightly disordered buttons that betrayed his early start, but I confess even I could not see the clues that led him to deduce that our visitor had run into trouble on the street that morning. I did not doubt, however, that they were there.

Gruen's broad mouth pinched in displeasure, but he sat down, his bulky frame out of place in the cluttered cosiness of our living room.

"I have a sister," he began, "who I stay with when I'm ashore for a while. She lives north of London, working as a maid for a professor who lives out that way. It happens that it's been nearly two years since I last saw her, and in that time, she's changed, almost as if it had been ten times that. She is younger than me by many years, but from our looks now, you would think me the younger."

Gruen's voice darkened as he spoke, anger clouding his brow. "I know it must be something horrible, probably from that professor, but she refuses to speak to me about it. Told me to leave it be, practically begging me. I hate to disappoint her, but I can't see her like that and not do something."

"Has the young lady a husband?" Holmes asked, steepling his fingers.

Gruen shook his head. "She lives with another of the housemaids and our father. The girls have been friends for years, and they both adore our father. His mind is not what it was, but he still has all the strength of his years in the merchant navy."

"The other maid, is she similarly affected?"

He shook his head again. "Bertie is the same as ever, though perhaps quieter. I believe she is also worried for my sister." He hesitated, then continued, "There is one more thing I should mention. I think she may be hiding something."

Holmes betrayed nothing, his eyes half-closed as he stared at his steepled fingers.

"She's been going out at odd hours with something clutched in her hand, then returning, empty handed, with an expression of guilt. She's like another sister to me, and I can't believe she would be willingly involved in hurting Violet, but it would be equally foolish to assume there's no connection." Gruen seemed to suddenly grow impatient. "Will you take my case or not?"

"Certainly." Abruptly, Holmes leapt to his feet. "Up for an afternoon's outing, Watson? I dare say it will not take much longer than that to clear this up."

Gruen snorted a disbelieving laugh as he led the way out the door. "Bold words, Mr Holmes, but I hope you can carry them through."

A few hours later, we arrived at the house of Gruen's sister. It was a pleasant little cottage, built in Tudor style, with daisies peeping at us from the garden bed. As we walked up the path, we could see a shed out the back, with the door firmly bolted shut. Over the door was a hand painted sign, spelling out 'The Old Boat'.

"A recent addition?" Holmes asked Gruen, nodding to it.

"The door's freshly bolted," he confirmed. "The shed's old, and full of Dad's souvenirs. Bertie said there's been a problem with cats in the neighbourhood getting into everything, so she bolted it up."

"Watson is a capital look out, I'm sure he can keep the cats away." Holmes smiled mysteriously and left the path, heading towards the little shed. Once we were close enough, he arranged the three of us around the door, offering no explanation. I began to hear a rumbling come from inside.

"Ready?" He asked, and at our nods, unbolted the door and threw it open.

We had a flash of a snarling white beast coming towards us, claws extended, when Holmes shut the door again, exerting his full strength against it.

"There's your beast!" he exclaimed. "Kept in the shed, and fed faithfully by its loving mistress."

Gruen's face was pale, and he stammered before asking, "What was that creature?"

"A cat."

The colour was beginning to seep back into his face. "I assure you, Mr Holmes, I have seen cats before. My ship has three good mousers. That, sir, was no cat."

"And I assure you, my dear sir, that was a cat." Holmes grinned impishly. "An unusually large cat, but nevertheless, a cat. Here comes its mistress now to confirm."

A young woman came up the path, then saw us at the shed and broke into a run. "John! John, leave it alone! You don't need to know."

"We already do."

At Holmes' words, the young lady came to a halt. Her bright face was a picture of confusion. "How?"

"Deduction, Miss Bertie."

Her eyes widened in astonishment, then she laughed. "I suppose John told you who I was!"

"He didn't need to. Who else would have kept the cat in the shed? You didn't bring it indoors, most likely to not upset Mr Gruen with his fragile state of mind, but you could not resist keeping it in some way. By going out to feed it every night, it's become quite friendly with you."

"It was so wet and lonely, I had to look after it," she confessed. "I didn't want Lettie to have to keep it secret, but I think it might have helped her to have a creature to pet. She's been looking so scared lately."

"Bertie!" A scream brought all our attention back to the path. Another young woman was standing there, face painted with anguish. From their similar colouring, she was clearly Gruen's sister. "Bertie, close the door!"

The door swung open, pushed from the other side by a very large white cat. It happily purred at its mistress, slinking around her legs. Bertie leaned down to ruffle its fur affectionately. "Have you missed me, you old monster? I'm sure you have." She called over to Violet, who was running towards her. "I'm fine, Lettie!"

"Bertie!" Violet ran into Bertie's open arms. "I was sure Father had caught some kind of snow leopard and was keeping it there! I was so afraid you would be attacked!'

"Oh, Lettie!" Bertie stroked the other woman's hair affectionately. "I never meant to frighten you. Will you forgive me?"

From the expression on Violet's face, it was quite clear she already had.

Prompt from Wordwielder: An adventure on a boat and from mrspencil: a snow leopard. A bit loosely interpreted, but hopefully enjoyable!