Ever-eclectic in her borrowings of style and substance from the best English mysteries, Grimes (The Dirty Duck, Jerusalem Inn, etc.) makes her latest a real jumble: part psychosexual gothic (Ö la P.D. James), part sentimental tragicomedy, part eccentric farce--with far more satisfaction in the separate parts than in the unconvincing whole. The story begins very Inspector Morse-ishly--as somber Supt. Jury fails in love with lovely widow Jane Holdsworth, only to lose her almost immediately: Jane commits suicide by overdose--or is it murder? To find out which, Jury sends his amateur sidekick Melrose Plant up to the Lake District, where the wealthy Holdsworth clan resides--headed by irascible Adam, 89, whose beloved poet-grandson (also a suicide) was Jane's husband. Is someone perhaps killing off all of Adam's favorite relatives for inheritance purposes? If so, then Jane's 16-year-old son Alex--a grieving would-be sleuth--may be in danger. Alex's moody encounters with teen-aged cook Millie (child of another suspicious suicide) are gently affecting; old Adam's capers at a local retirement-home are giddily amusing; there's a whole gallery of fetching characters. But the pieces never come together effectively. Nor does the plot--which involves too many family secrets and oblique motives. Still: superior page-by-page entertainment from a skillful imitator.