From 1930, THE SAINT CLOSES THE CASE would be in modern parlance a fix-up novel. It was initially two separate stories published in THRILLER magazine in 1929. Charteris took a chunk out of the first story and dropped the second in the middle, of course doing some re-writing to smooth things over.
The tale concerns Simon Templar and his lady Patricia stumbling upon a demonstration of a new weapon of mass destruction. The Saint is appalled and determines to stop this weapon. The world is still getting over the Great War and the millions sacrificed to then new weapons of tanks and machine guns.
Opposing him is Dr. Rayt Marius in this, the first of a loose trilogy with the
villain. He grabs Patricia in a bid to get the scientist and his device, necessitating a rescue.
The Simon Templar of this early story is not the genteel fellow of later stories. He’s perfectly willing to kill the scientist if he can’t be persuaded to abandon development of his super weapon.
The first title it was published under was THE LAST HERO and occasional editions over the years have used it. One of Amazob’s publishing arms, Thomas & Mercer, is putting out uniform cover editions with introductions by prominent authors in the mystery field.
Excellent.
Not The Baseball Pitcher 
Glad you mentioned previous titles. I have this one, under the “last hero” title. Haven’t read it though.