at the corner of the street i dismissed the cab, and hurried after a familiar figure. it was sophy, who seemed to be literally flying along the pavement, now on one leg, now on the other, and had she not suddenly wheeled round in my direction i should have had to run at the top of my speed to catch her. seeing me she pulled up, and, with her face scarlet with excitement, greeted me boisterously.

"why, what on earth are you doing, sophy?" i asked, laughing and wondering at her.

she lifted her feet, one after another, for my inspection; she was skating on wheels.

"i'm the champion skater," she said, triumphantly; "i shall git a turn at the music halls before long. look 'ere; i can beat the lot of 'em."

away she flew with marvellous swiftness for a space of fifty yards or so, then wheeled round and round and reached my side by executing a series of circles in the cleverest manner possible. i have no doubt that there are technical terms to describe her feats, but i am not acquainted with them.

"there!" she cried. "what do you think of that?"

"you'll break your neck if you don't mind," i said.

"break my neck!" she exclaimed. "not me! that's nothink to what i can show yer. i am glad to see yer back, i am? aunty sed you'd give us up. 'not 'im,' sed i; 'he ain't one of the giving-up sort.' you look tired out; ain't yer been well?"

"quite well, sophy, but, like you, very busy. is your aunt at home?"

"yes," said sophy, bursting into a fit of laughter; "she's down in the kitching, with a pore man's plaster on 'er side. i got 'er to put on the roller-skates--leastways i put 'em on for 'er--and the minute she stood up in 'em she toppled over and fell agin the dresser. she ain't 'urt much, but she likes to make a lot of a little. i'm all over bruises, i am, but i don't fuss over 'em."

"you shouldn't play tricks on her," i said gravely; "she has been a good friend to you."

"oh, i don't know about that," said sophy, with a rebellious toss of her head. "she makes me pay for it, nagging at me morning, noon, and night. but there, i ain't going to say nothink agin 'er. she's got a temper, and so 'ave i."

"she has been greatly worried, sophy; you must be gentle with her."

"i'll do anythink you tell me; you don't bully a gal, you don't. if you told me to go and jump off the top of the monument i'd do it--yes, i would, though you mightn't believe me."

"i shall not ask you to do anything so stupid, but you can render me a service, if you have the will and the pluck."

"can i?" she exclaimed, eagerly. "i ain't much to look at, but i've got the pluck of a big 'un. only you tell me what it is."

"it will first depend upon whether your aunt can spare you. we will go in and see her."

"she'll 'ave to spare me, and if she don't like it she may lump it. now i know yer want me, i ain't going to let yer off."

"you appear anxious to serve me, sophy."

"i'm going to serve yer," she said, with emphatic nods. "there's nothink mean about you. when a gent makes a promise he sticks to it."

"a promise, sophy!"

"didn't yer promise yer'd give me somethink to do for yer--and didn't yer say jest now it depends upon whether i've got the pluck to do it? that settles it. i've got the pluck, and the thing's as good as done. nobody in all the world 'as been as good to me as you've been, and it ain't likely i shall ever forgit it. you'll see. one day when i'm somebody," and here the grateful girl gyrated round me gently, and really with grace--"yer'll be proud of 'elping me on, and then i'll show yer i can remember."

"your aunt can't be left alone," i said, after a moment's consideration. "do you know of any girl or woman who would take your place here while you are away for a week or two?"

"i know twenty that'll be glad of the job. i'm to go away, am i?" her eyes glittered at the prospect of an adventure. "i'm ready this minute where to?"

"i'll tell you all about it after i've spoken with your aunt. it isn't an easy task i shall set you, sophy."

"the 'arder it is the better i shall like it."

"do you think you could play a part?" i asked.

"on the stage?" she cried, eagerly.

"no; off the stage."

"on or off," she said, with a shade of disappointment, "it don't matter. i'm game for anythink. let's git aunty settled fust."

sophy, being now provided with a latch-key, opened the street door, and taking off her roller skates in the passage, preceded me down-stairs. mrs. middlemore was darning stockings, and seemed cheerful enough, but when she looked up and saw us her face assumed a colorless expression, and she pressed her hand to her side. sophy winked at me, and said, in a whisper, "she's putting of it on; she ain't 'urt a bit, no more than you are."

"oh, good evening, sir," said mrs. middlemore, mournfully. "what are yer whispering about, sophy?"

"only telling the gent," replied the unblushing girl, "not to speak too loud, 'cause of yer nerves, aunty."

"it's all sophy's doings, sir," moaned mrs. middlemore. "she made me put on a pair of rollers that's going to break 'er legs afore she's done with 'em. she's a double 'andful, sir; i can't manage 'er."

"she has told me of the accident," i said, "and is very sorry for it. sophy means well, mrs. middlemore."

"i won't dispute with you, sir, but she'll be the death of me if she goes on as she's a-doing of now. you've been away a long time, sir."

"not so very long; i had important business in the country to attend to. nothing has happened, except your accident, during my absence, i suppose?"

"nothink as i can think of, sir."

"no more visitors in disguise; no more false summonses to the police court?"

"no, sir--only i've got my fancies."

"what kind of fancies?"

mrs. middlemore looked timorously around, and sophy answered for her. "there's a sperrit in the 'ouse, she ses. she 'ears it moving about, and she's ready to swear in the middle of the night that it's a-standing at the foot of the bed."

"do you also hear and see it, sophy?" i asked.

"not me," replied sophy, contemptuously. "it's a wide-awake sperrit, and makes itself scarce when i'm about."

"ah, well," i said, "there's no accounting for fancies. let us get to business, mrs. middlemore. i intend to rob you of sophy for a little while."

"rob me of sophy, sir!" exclaimed mrs. middlemore. "what on earth am i to do without 'er?"

"oh, you will get along very well without her----"

"but you don't know what a 'elp she is to me, and 'ow good she's been. i've got that fond of 'er that i don't like 'er to be out of my sight. you're joking, sir, ain't yer?"

"not at all," said i, smiling at this sudden display of affection. "i have something for sophy to do, and if she undertakes it she will get well paid for the job."

"never mind about my being paid for it," interposed sophy; "i'm going to do it, whatever it is."

"and leave me 'ere all alone!" whimpered mrs. middlemore.

"you will not be alone. the first thing in the morning a girl shall be engaged to keep in the house with you, and i will pay her wages; and you shall have an allowance while sophy's away. remember what i have done for you, and don't make any further objections."

"i'm sure you've been very good, sir," said mrs. middlemore, her trouble lessened by the prospect of gain; the virtues of golden ointment are not to be excelled. "might i take the liberty of arksing whether it's got anythink to do with mr. felix?"

"i cannot answer you," i said. "what sophy will do will be a secret between her and me for the present. by and by, perhaps, she will tell you all about it."

"you've got a way with you, sir, that nobody can't resist. you'll come back to me, sophy?"

"course i will, aunty," said the girl, "when the job's done."

"and now, sophy," i said "if you will come upstairs with me we will have a little chat. then you can decide."

"i've decided already," said sophy, and she followed me to the sitting-room which had been occupied by m. felix.

everything apparently was the same as on the night of the disappearance of m. felix's body. i was aware of only one article which was missing after dr. peterssen's visit to the house, and that was the revolver which m. felix kept under his pillow. i had no doubt in my mind that dr. peterssen had taken advantage of his being alone in the house, on the occasion of mrs. middlemore's unnecessary visit to the bow street police station, to appropriate other articles, but only the revolver and the desk--which he had taken away on the night of his interview with m. felix--were within my knowledge. it is true that even this knowledge was gained by means of circumstantial evidence which would scarcely have been admitted in a court of law, but i was quite satisfied on the point, and i had the strongest moral conviction that time would prove the correctness of my conclusions.

"sit down, sophy," i said, "and think of nothing else but what i am about to say to you."

"i'm a-doing of it," said sophy, with a look of absolute concentration that strengthened my confidence in her, and spoke volumes in favor of her being, as she hoped, somebody one day.

"you remember the day on which your aunt was sent to bow street police court by a man whom she left in the house alone?"

"yes, i do."

"you said you saw the man. would you know him again?"

"i'd swear to 'im."

"on the night that mr. felix's body disappeared you were the only person in the house who knew anything at all of the matter. you behaved like a little heroine on that occasion, sophy."

"that's something good, ain't it?"

"something very good. there is no possibility, i suppose, of your being able to give me a description of the man who, by some strange means, got into the house on that night?"

"i can't tell you nothink more about 'im. it was in the dark, yer know, and when he spoke it was under 'is breath."

"the question was an idle one, but i was bound to ask it. it may or may not have been the same man who deceived your aunt. sophy, the man you saw and can swear to is an infernal scoundrel, and i look upon him as my enemy."

"that's enough for me; he's mine, too, and i'm 'is."

"you can keep a secret, sophy."

"you tell me one, and wild 'orses sha'n't tear it from me."

"you are a faithful little soul, and i put great trust in you. everything i am saying to you is a secret."

"that's enough," said sophy, touching her lips with her fingers. "red 'ot pinches shouldn't git it out of me."

"the man you saw was in this house, to my certain knowledge, once before--while m. felix was alive. your aunt did not know it; m. felix opened the street door for him. it was the night m. felix was found dead, and when the man went away he took a desk with him that belonged to m. felix."

sophy nodded. "aunty's spoke to me about that desk. she never could make out, she ses, what 'd become of it."

"i will describe it to you, sophy." i did so, and she listened attentively, nodding from time to time with surprising intelligence. "if you happen to see this desk in the possession of the man whom i look upon as my enemy, do you think you could identify it?"

"know it again? yes, i should. but 'ow am i to git to the man?"

"i have thought of a plan, or rather a friend of mine has, which requires courage to carry it out successfully. it requires something more than courage; without great good sense and coolness the plan would fail. the question is whether you possess those qualities."

"it ain't no question at all; i've got what you want, and can do what you want."

"there is something in the desk, sophy, that is of the utmost importance to me."

"and i'm to git it for yer. all right. smuggle me into the 'ouse, and consider it done."

"but you don't know what kind of a place it is, my girl. it's a private madhouse." sophy did not blench; she simply nodded, and fixed her large brown eyes on my face. "the man's name," i continued, "is peterssen, dr. peterssen. if he wanted a young girl as a servant you should apply for the situation, but i don't think there is a vacancy in his establishment. he is ready to take more patients, though, and he likes young patients better than old ones."

"you're going to put me in there as a mad gal," cried sophy, in a tone of irrepressible excitement, which lasted, however, only for a moment. she cooled down instantly, and said in her usual tone, "crikey! that's a good move. i'm game! it's a good part to play, and no mistake."

"you'll do it, then?"

"do it? won't i do it? why, i never thought i'd 'ave sech a chance."

"you will have to be respectably dressed, sophy, hands and face nice and clean, and hair very tidy. how long in the morning will it take you to do that?"

"you git me the clothes and i won't keep yer waiting. i'll give myself a good scrub to-night."

"i've only one fear for you," i said, "which you won't mind my mentioning. going as a girl in a respectable position, your language might draw suspicion upon you. i can't see a way out of that difficulty."

"i can," said sophy, with a merry twinkle. "why should i speak at all? let me go as a dumb gal. it'll be more than ever they can manage to git a word out of me if i was there for a year."

i looked at her admiringly. her sharp wits had solved a problem which had greatly perplexed me.

"you are sure you will not be afraid, sophy?"

"not a bit afraid; i shall enjoy it. it'll be a reg'lar game."

"very well, then. you can sleep upon it to-night, and if you alter your mind you can let me know. i shall sleep here myself, and shall be up early in the morning. there will be a great deal to do, and no time must be lost. goodnight. say nothing to your aunt."

she nodded smilingly, bade me good-night, and left me to my reflections.