Prompt: I laughed at this cross-examination. "I keep a bull pup," I said, "and I object to rows because my nerves are shaken, and I get up at all sorts of ungodly hours, and I am extremely lazy. I have another set of vices when I'm well, but those are the principal ones at present." - What exactly was that other set of vices?

A/N: Just watched DANC last night, which gave me this idea when I read the prompt... I couldn't think of any other good vices for Watson, so I just focused on the one.

Sherlock Holmes came bounding into the sitting room, in one of the best moods I have ever seen him. I have become accustomed to his mood swings; the periods of calm in which he is moody and ill-tempered, the fierce energy he exhibits when hot on the trail of some criminal, the hours of quiet contemplation with his pipe and violin. This evening marked the end of a particularly knotty problem, which he had just brought to a satisfactory conclusion, and he was feeling justifiably elated. I thought it likely that his habits during the case would catch up with him later tonight, considering he had, as always, neglected food and sleep during the investigation. For the moment, however, he was quite energetic.

"A most intriguing little problem, Watson!" he said excitedly, rubbing his palms together in a satisfied manner. "I would advise it's admission into your little record of publications--there were certain points of merit which would certainly be of some interest to your readers."

My friend's good mood was infectionous, and I found myself smiling at his jubilance. "How exactly did you know that the man's brother had been in the house that day?" I asked.

"The mud, Watson. That particular reddish hue that was present in great quantities surrounding the doorstep during the recent remodeling. He had taken care to brush it from his shoes before coming to join us but not, I noticed, from the cuffs of his trousers. No doubt he is now wishing he had taken more care to keep his clothing immaculate, as he usually does." Holmes cheerfully flung my coat in my direction. "Dinner at Simpson's, Watson?"

My good mood evaporated, and I could feel myself blushing. "I... I can't, Holmes."

He paused in donning his jacket, and raised an eyebrow. "Why ever not, my dear fellow?"

I thought frantically for a moment. "I'm afraid I have a bit of a headache coming on--I should probably just stay here and rest a bit," I muttered.

He stared at me a moment, then crossed the room to sit on the arm of his armchair and look me in the eye. "My dear Watson, falsehood does not become you. What is going on?"

I was about to repeat my headache excuse, but he cut me off. "Watson, in all the time I have known you, you have never complained of a headache unless you were in the midst of a migrane that would have floored a lesser man. Furthermore, when you do have a headache you have a habit of pinching the bridge of your nose, which you have not been doing. Something is troubling you, and I should be much obliged if you would tell me what it is."

I did not meet his eyes. "I'm completely broke, Holmes. I couldn't possibly afford to go out--"

"Is that all?" He clapped me on the shoulder. "It's my treat, my dear fellow."

"Holmes, I couldn't--"

"Nonsense, Watson! The conclusion of this latest case has left me with a pretty sum, and what better way to spend it than on dinner with a friend? Come, Watson, accept a spot of charity this once, and I shall have your company as recompence." He shouted downstairs for Mrs. Hudson to call us a cab, and handed me my coat again, and I felt I could do nothing but accept.

"How did you come to be in this strained position in regrads to your finances?" he asked, as we sped towards Simpson's. In another man this question might be considered insensitive, even offensive, but coming from Holmes it was the kind of inquiry he made as a result of his thirst for exact knowledge. The answer, however, was rather embarassing to me. "It was the card game last night," I finally admitted, feeling myself reddening again. "I'm afraid I was... less prudent than I ought to have been."

He gave me a small half-smile. "Come now, Watson--you are surely not the only person to have found yourself in such a predicament. It is a little unusual for a man of your careful tendencies," he continued offhandedly, completely unaware that I already knew of this incident's contrast to my character and was thoroughly embarassed by it, "but overall really, Watson, it is a rather trivial incident."

His good cheer was impossible to combat, and as the conversation drifted to other matters I forgot the matter, though I was embarassed when Holmes picked up my share of the check.

Two weeks later I was in low spirits, having lost more than I could afford to my fellow card-players the night before. Holmes was working at another chemical experiment, which I fervently hoped would not have the same effect on our curtains that it had last time. I had thought him completely immersed in his work, but suddenly his voice rose from the plethora of test-tubes and beakers. "Bad night, Watson?"

I started, then stared. "It was, Holmes. How did you know?"

He turned. "My dear Watson, I should hope that our years of shared living space would give me some sense of your moods. You were far from jubilant last night, and remain subdued this morning. Thus, I concluded that last night did not go well for you, for some reason."

I flushed again at his statement. "I was betting rather more heavily than I ought," I admitted. It was more embarassing to me than might be readily apparent, for I prided myself upon being a level headed, sensible man. To continually lose sums which were outside my means was not only foolhardy, it put a blemish on my character that I felt humiliated to have revealed.

Holmes seemed to understand this, somehow, despite his usual obliviousness to the embarassment of others. "My dear Watson, you are among the most sensible of men," he said with uncharacteristic gentleness. "The matter should not be attributed to a lack of judgement in all things."

"Thank you, Holmes," I said, genuinely comforted. "It would mean less to me if it did not happen repeatedly, but it seems I am less of a prudent man than I thought I was when it comes to betting."

He thought for a moment. "Perhaps, Watson, we can arrange matters to be less of a risk to your finances."

My checkbook has been locked in his desk drawer ever since.

A/N: How do I write my stories, you ask? Apparently I write half of one as soon as I get the prompt, then lose my train of thought and let it sit for the rest of the day before coming back to it. DON'T DO THAT. IT'S BAD FOR THE BRAIN.
I figured there had to be a reason why Watson's checkbook was locked in Holmes' drawer. So that's where the idea of gambling as a vice came up. For more on that read Chewing Gum's fic, which is awesome and much better written.