Complex sentence: In 1955 Christie was the first recipient of the Mystery Writers of America's highest honour, the Grand Master Award, and in the same year "Witness for the Prosecution" received an Edgar Award by the MWA for Best Play.
Split into simpler sentences: In 1955 Christie was the first recipient of the Mystery Writers of America's highest honour, the Grand Master Award. Later the same year, "Witness for the Prosecution" received an Edgar Award by the MWA for Best Play.