Just what we all needed--an sf novel set at an sf convention. The narrator is a reporter with marginal telepathy or serendipity or something that always plunks him down at the scene of a story--here, the murder of a well-known ESP debunker -- with improbable accuracy. There's a black folksinger who's an ""emotion dowser,"" and a crowd Of fans in captain Marvel-ous costume, and a lot of woodenly introduced aficionado lore . . . . Is sf really that hard up for ideas these days?