Complex sentence: Around 1941--42, the British intelligence agency MI5 investigated Christie after a character called Major Bletchley appeared in her 1941 thriller "N or M?", which was about a hunt for a pair of deadly fifth columnists in wartime England.
Split into simpler sentences: Around 1941--42, the British intelligence agency MI5 investigated Agatha Christie. A character called Major Bletchley appeared in her 1941 thriller "N or M?", which was about a hunt for a pair of deadly fifth columnists in wartime England.