Lay On, Mac Duff!

{{Short description|1942 novel}}

{{Use mdy dates|date=March 2025}}

{{infobox book

| name = Lay On, Mac Duff!

| title_orig =

| translator =

| image =File:Lay On, Mac Duff.jpg

| caption =

| author = Charlotte Armstrong

| illustrator =

| cover_artist =

| country = United States

| language = English

| series = MacDougal Duff

| genre = Mystery

| publisher = Coward-McCann

| release_date = 1942

| english_release_date =

| media_type = Print

| pages =

| isbn =

| preceded_by =

| followed_by = The Case of the Weird Sisters

}}

Lay On, Mac Duff! is a 1942 mystery novel by the American writer Charlotte Armstrong. It was first published in New York by Coward-McCann, an imprint of Putnam.Reilly p.43 The first of a trilogy featuring amateur detective MacDougal Duff, it was followed by The Case of the Weird Sisters (1943) and The Innocent Flower (1945). The title is a punning reference to both the protagonist's name and a line from William Shakespeare's Macbeth, with the following two titles in the trilogy also referring to the play.Cypert p.55 It was Armstrong's debut novel, following two Broadway plays that made no great impact.