Charles Marowitz's play Sherlock's Last Case predates Michael Dibdin's The Last Sherlock Holmes Story by about three years [EDIT: somehow botched the dates in the original post!], and both adaptations (or appropriations, really, given the extent to which they rework the source material) share a wry-to-dark assessment of Holmes' indestructability as a Victorian superhero. In Sherlock's Last Case, which continually reminds us that it is a "melodrama," a homicidal Watson tries to murder Holmes in a bleakly hilarious Rube Goldbergesque scheme, only to find in Act II that Holmes managed to escape in equally ludicrous fashion (involving, amongst other things, his trademark pipe). But this Holmes and Watson are, the casting directions tell us, explicitly in the Rathbone/Bruce mold; the homicidal Watson is an adapted Watson, trapped in a state of melodramatic buffoonery. The play, that is, is not so much about ACD's Holmes and Watson as it is about what has happened to Holmes and Watson in the wake of the WWII-era films. (As I pointed out to my students, Watson's conclusive evidence that the impostor-Holmes-who-is-really-Holmes is a fake--that Holmes asks Watson's advice--is, in fact, entirely wrong if you think about this play simply in relation to the original stories.) And it is also about the very real problem posed by a dramatized Watson, as he immediately loses his plot function once he and Holmes share the screen. In the play's rather sadomasochistic account of the relationship, Holmes finally "wins" by tricking Watson into admitting that his loathing is "a perverse kind of love" (70)--a revelation that also demonstrates Watson to be the only character in the play capable of feeling. Everyone else in the play is shallow (Mrs. Hudson), utterly incapable of acknowledging other human beings as thinking and feeling subjects (Holmes), or manipulatively theatrical (Bertha). But this moment also flips Holmes' famous outburst in "The Three Garridebs," in which Watson finally has proof that Holmes truly cares for him; instead, Holmes treats Watson as a character in an elaborate performance designed for domination. As one of my students perceptively noted, Holmes effectively ends the play aspiring to be his own narrator, even though he keeps Watson around to "chronicle the events" (62).
It's not clear if Dibdin knew Sherlock's Last Case, but one can't help noting that The Last Sherlock Holmes Story also features a Watson trying to murder Holmes, for very different reasons. In Dibdin's novel, Holmes turns out to be existing in an alternate mental universe, built out of an elaborate conspiracy theory involving Jack the Ripper (guess who he turns out to be?) and Moriarty. It is Watson who successfully investigates Holmes, but the initial block to this investigation is his belief that "Holmes is above all a great champion of the law--the great champion" (128). At stake, in other words, is not Holmes in and of himself, but Holmes as a cultural icon. Justifying his decision to act as Holmes' executioner, Watson insists that "[t]he abomination Holmes had become threatened everything I hold dear and by which I have lived my life. The last thing I wished was to see such filth besmirch for ever the image of a man whom others besides myself had come to regard as among the best and wisest England had ever known. It would have been a terrible and damaging blow to the moral fibre of the entire nation if Sherlock Holmes had been identified in open court as the author of these lines" (165). The ambivalence here--Watson had just compared himself to Judas (165), and much earlier, in a moment of foreshadowing, to Brutus (89)--suggests a more psychologically realistic version of the tension informing Marowitz's deliberately overheated play. Watson decides to kill Holmes in order to save the very foundation of his own worldview from fatal contamination, but also to, in effect, martyr him, to destroy the living murderer in order to canonize the literary saint. Killing Holmes will make him the superhero he has actually ceased to be (and, Watson realizes, never really was). Moreover, the emphasis on "moral fibre" harks back to the WWII-era films again, in which Holmes was truly an English national hero preserving the country from evil (Doylean and otherwise).
And then, there are the endings, which I will put beneath the fold.