“A Problem in Adultery” might aptly be the subtitle of Ellery’s latest case. Who is pretty Mrs. Lawrence’s lover? And how can the young, rich Broadway producer be saved from the folly of her infidelity and the fury of her husband Dirk, the unsuccessful author who cannot control his morbid attacks of jealousy? These are Ellery’s major problems. Beginning with a night rendezvous in the park and a punch in the jaw from Irate Husband, Ellery finds himself hot on the trail of an unknown Casanova... suspected lover, home-wrecker, and likely target for a .45. And making the trail all over the jungle of New York City — from Chinatown and The Bowery to the upper reaches of Bronx Park — are the tantalizing Scarlet Letters, an alphabetical puzzle that keeps Ellery — and the reader — cudgeling his wits to the very end. Ellery has a special surprise for you in a case as sensational as the front page of tomorrow’s tabloid — the first appearance in a Queen novel of Nikki Porter as Ellery’s Girl Friday, that fiery, faithful, and long-suffering secretary of the Queen radio and short-story adventures. But THE SCARLET LETTERS is full of surprises, not the least of them the astounding pay-off of as exciting and clever a mystery as Ellery has ever gone a-hunting