After some up-and-down tries at detective fiction, Dewhurst made a limp stab at espionage (Whoever I Am)--and now lurches into vaguely gothic murder-suspense. Sue Lester, 16 and fatherless, has been--since babyhood--a cast member of Britain's longest-running soap, ""The House That Jack Built""; and Sue shares her affections almost equally between her cool, intellectual mother Sonia and her warm-hearted House mother Meg--when not writing embarrassingly adoring thoughts about co-star Ralph Boyd (handsome, unresponsive) in her diary. Then the diary vanishes--and soon a disguised telephone voice threatens Sue with its publication unless she performs some seemingly harmless tasks. But when Sue complies, her actions tie her to a series of nasty cast mishaps, culminating in the murder of Meg's sister Audrey. And it looks like Sue will be framed for the crime--until her mother comes through with a hackneyed trap to catch the murderer (and unveil an out-of-the-blue motive). Despite some strenuous efforts at Sue's characterization: talky and unexciting, with an uninteresting juvenile heroine and a cut-out supporting cast.