Technically, Murder in the Cathedral by T. S. Eliot, does not portray modern drama, as it is not a play about the making of modern plays, but instead it is a modern drama, and can be said to "exemplify" some of the features of modernism.
In some ways, Murder in the Cathedral is just as much a rejection of the earlier "modern" drama of the nineteenth century and a return to pre-modern dramatic forms as it is something distinctly new. The key feature of the play that is both modern and radically traditional in its rejection of realism, both in its language and its narrative.
The most distinctive feature of the language is the return to verse (and heightened language in general), which had been the dominant medium of drama from antiquity through the Renaissance, but was abandoned with the rise of realism. In terms of narrative, Eliot moves away from the realistic portrayal of the everyday events in the lives of ordinary people to a highly stylized narrative that externalizes the inner and symbolic conflicts in religious faith Returning to the medieval morality play for inspiration, Eliot presents speakers without names, who make present on stage ideas or types of moral nature, rather than characters. It is this rejection of realism that makes the play "modern."