Austin J. Small (1894-1929) was a popular British mystery and thriller writer who was published in the United Kingdom under the pseudonym "Seamark".
"The Man they couldn't Arrest" - written in 1925 - is a fast paced thriller about Valman Dain, an inventor who (amongst numerous other intriguing gadgets) develops a mechanism for eavesdropping on conversations using the telephone network. Using this technology, Dain sets about tracking down and identifying the various criminal gangs which are plaguing London and sending anonymous tip-offs to Scotland Yard. The hitch is that Scotland Yard is convinced that only a master criminal himself could gather this much information about the gangs... and they focus their attention on finding the anonymous tipster. The criminal gangs too are soon hot on Dain's heels, when he accidently gives his identity away to one of them. But Dain's problems are about to get much worse. He discovers that one of the gang leaders is Willard Lyle, the father of Mercia Lyle - the girl he hopes to marry. And Willard Lyle is on his way to Dain's house with murder in mind...