Okay, technically this is more a movie than a play, but given it's an adaptation by Nigel Kneale, I'm going to let it off.
A 1983 horror novella written in gothic style by Susan Hill, The Woman in Black concerns a mysterious ghost that haunts an English seaside town, heralding the death of children. Largely an investigation by solicitor Arthur Kipps, it follows his attempts to discover who the mysterious woman he sees around town is. Let's just say he's not pleased by the discovery.
Adapted more recently by Hammer Horror with Daniel Radcliffe in the starring role and more famously as a play in the West End, where it's the longest running show after The Mousetrap, it was adapted for television by Nigel Kneale back in 1989. Despite featuring Adrian Rawlins as an 'Arthur Kidd' (sic), it was a considerably more faithful adaptation than the movie or the play. And you can watch it below, preferably in the dark.