This is the first the bow knows of his peril:
The lid of his case opens, revealing his snug nest to the light and the air, and he eagerly pushes out a figment of a song to Sherlock. It is both a greeting and suggestion — a caprice, light and playful. He's in a fine fettle today, and hope blooms bright that Sherlock will accept the suggestion: he would enjoy the feel of Sherlock's hand, lithe and strong, as they work to meet Paganini's inventions; the delightful effort of the music itself, the music always demanding just a bit more than their abilities; the fine bloom of moisture on his frog and pad as Sherlock works up a sweat over the music; the languid rub-down with a soft cloth, after. It would be delicious. It has been far too long since they've indulged in such a hedonistic air, and the bow pushes all his joyful anticipation into that scrap of music. At the least, he expects a chuckled "Cheeky…!" but he gaily hopes for so much more—
He stops in confusion. The human is not Sherlock.
The confusion only deepens when it appears that Sherlock is nowhere nearby. As a rule, Sherlock is jealously protective: very rarely, Sherlock will permit someone to open the violin case in his stead, but he is always there, hovering in the background, ensuring that the interloper takes no liberties with his precious bow.
And yet, no matter how the bow reaches for that warm and familiar presence: there is no Sherlock.
It is, at the very least, unsettling.
A strange hand reaches into the case and strokes his stick, and he lies resentfully under the alien touch. He has known the touch of salesmen, technicians, and other violinists — there have been so many other violinists than Sherlock in his long life! — but this is not the knowing and confident touch of a skilled person. Yet neither is it the wondering, reverent touch of an appreciative novice. Altogether, there is something decidedly off about the touch: inexperienced, to be sure, and yet still insolently bold, too willing to leave clumsy fingerprints all over something it knows nothing about…
Then the finger strokes his hair, and the bow vibrates with the utter, inexpressible wrongness of it. The bow squeals its distress and revulsion— The touch continues, even rubbing the hair between thumb and forefinger. Again, the bow cries out, a discordant screech of shock.
Then the hand removes itself to stroke the violin's wood, and the bow can feel that the brute violin, already uneasy from the bow's distress, is further unsettled by the wrongness in the stranger's touch. The bow vibrates in helpless sympathy, unable to protect it.
Then the hand withdraws and the case shuts, the latches snicking into place, and both violin and bow are left alone together in the dark. Case, bow, and violin are all lifted, swinging freely with a human stride, and once more the bow cries out for Sherlock—
Once more, there is no response.
The bow lies quietly under his clip, the oily residue of that ever-so-wrong touch clinging to his hair, and sings to himself. It is a mournful song of the lost lover, a plea for reunion, a hope of deliverance.
The violin has borne the brunt of the interloper's attentions to date. It is short a string now, or most of one: the E-string violently cut away with a pen-knife, its two ragged ends trailing disconsolately from bridge and peg. The violin is confused and bewildered by the indignity, but no real damage has been done. Someone will eventually come along to restring it; someone always does.
The bow sings in search of strength to lend to the injured violin, and in the process of lending his strength, finds strength for himself. The violin is too stupid to understand the interloper's intent, but the bow has heard and understood the man. The interloper will come for the bow next; when he does, it will not be something so easily set right as some dirtied or cut horsehair.
The bow sings for courage: for Sherlock, for the violin, for himself. He sings of his hope of deliverance from Death.
In the end, it is not Sherlock who is his deliverance, but Mycroft.
The bow lies stunned and silent, his case open on Mycroft's lap under the glare of the fluorescents of the empty Tube car. He himself has never felt any sympathy with the unmusical Mycroft; if anything, he has only felt a snide superiority over him, pitying him for the absence of artistry in his soul. And yet in the end, it is Mycroft who has come for him.
"You're safe," Mycroft murmurs. "I'll take you to him directly. Have no doubt; he would have come himself, if he could."
The case snicks shut again, and the bow lies silently in its dark nest, reconsidering that soft voice.
Perhaps there is music in Mycroft's blood after all.
When the case opens again, it is not Sherlock, but the flatmate, John; the bow can sense Sherlock at the other side of the room, hanging back, reluctant to engage. John gingerly lifts the violin out of the case, leaving the bow behind, and after the tension of the previous days, it is altogether too much. The bow explodes in an exasperated snatch of Bartók, distressed and discordant, the fragment punctuated with pizzicato to emphasise his discontent.
There is no response from Sherlock.
Then to the bow's relief, Sherlock responds in kind. Or nearly in kind: an open pizzicato chord on the violin's remaining strings. It is repeated mindlessly, with increasing agitation. It's not even music, simply an exercise, and in it, the bow can hear Sherlock's distress, an echo of the violin's own. It is a sign of a sort of harmony between them, however prickly and uncomfortable it may be, and it reassures the bow. He lets the Bartók subside; in a few more moments, Sherlock and the violin go silent, too.
The bow waits, lonely and hopeful. He sings a few notes, tentative and yearning.
It is enough to stir Sherlock to action: he comes to kneel before the case; with trembling hands, he puts away the violin. He releases the bow's clip and runs a tentative, solitary finger along his stick. The frog, the tip, the ferrule… The bow relaxes into the knowledgeable touch. Sherlock ghosts his finger above the bow's hair, and for the first time, the bow's music falters — but Sherlock knows better than to compound the offense of the first touch with another. Time might remedy the dirty sensation in the bow's horsehair — time and rosin and music — but nothing else will.
Again, the bow sings quietly to Sherlock. He does not resent that Sherlock sent Mycroft for him: Orfeo would have done better to send another in his place, someone more cold-hearted and less like a lover, to rescue Euridice. Euridice might yet be alive, had Orfeo been so far-sighted.
The bow sings again, low and plaintive, a song of his faith in Sherlock, and this time Sherlock yields to the suggestion and takes up the violin. The missing string will be awkward, but they can work around it: the yearning for reunion is too intense to take the time to replace the string.
Sherlock takes up the bow in his long fingers, sets his horsehair against the strings. Tentatively, he tries the first notes of the bow's song.
Then together, they play.