A visit to the Plymouth sometime in the next few weeks can be justified on the grounds both of entertainment and of education, for "Angel Street" is a well-nigh perfect example of what a cracker-jack cast can do to rescue mediocre melodrama from becoming ridiculous. The play itself is just another mystery, complete with eerily fading gas-lights, a sex-hungry housemaid, and brooches with secret compartments. If read, it would be more an exercise in credulity than an experience in literature.

But three actors and actresses transform the drama into the most powerful production to hit Boston in many a season. Byron McGrath's portrayal of the vitriolic Jack Manningham will send chills jumping from vertebra to vertebra for three solid hours. His tortured, neurotic wife, as played by Lynn Phillips, is a study in desperate hatred. Relief from all this psychopathic tension is contributed by Ernest Cossart in the role of a detective, Sergeant Rough. Cossart has been appearing in movies for several years, but has always been buried in minor parts as a butler or valet. In "Angel Street" he reaches full stature, playing a tender-hearted sleuth with an ever-present bottle of Vat 69.

This cast manages to shatter the traditional aloofness of Boston audiences. Every time Manningham tries to strangle his wife and is foiled by the entrance of Sergeant Rough, a lengthy sigh rises from the orchestra and the balconies. At several points the staid Bostonians booed the villain and shouted directions at the hero.

Patrick Hamilton's play will neither be included in anthologies of English drama nor win a Critics' Award. It doesn't pretend to be a major work of art. But, for chilliness and clever acting, it's the best evening you'll spend for a long time.