The Plague Court Murders

The US William Morrow (New York) 1934 edition is the true first and precedes the UK Heinemann (London) 1935 edition by a year; this order is confirmed by the Sotheby's catalogue record, Wikipedia's publication data and dealer cataloguing. Both are collected — the Morrow as the true first, the Heinemann 1935 as the first British edition. Note for the Heinemann: per Quill & Brush, Heinemann's dated-title-page practice applies only to 1890–1921 and does not govern a 1935 book, so do not apply that rule here. Watch for the "first thus" trap of the modern American Mystery Classics reissue, which is a reprint, not an edition point.