In the stage play Black Coffee, Tredwell is the butler of Sir Claud Amory at Abbot's Cleve. Although he has relatively few lines, he appears frequently, having to serve drinks, being sent to summon people or having to show people in. Stage directions indicate that his part can be doubled with that of Constable Johnson. Tredwell assists Sir Claud in arranging his "scene" in the library. Tredwell locks the doors of the library with all of the family and house guests inside so that Sir Claud could confront them and demand that one of them who stole his formula should return it. Although it is not stated, it is likely to be Tredwell who switches off the lights at the desired moment.
Later, Tredwell is interviewed by Poirot. He tells Poirot his opinion that Lucia Amory did not really like the fact that Dr Carelli stayed for dinner. Carelli had turned up unannounced and Caroline Amory asked him to stay for tea and then invited him to dinner, thinking that he must be Lucia's friend. However Tredwell could tell by the look on her face that she did not like it.