Perhaps the dreariest of the full-length Saint novels.
Of the wartime stories, Charteris said (perfectly reasonably) that 1) to be at all credible, the Saint's contribution to the war effort had to be minuscule, and 2) he didn't want the Saint doing things more heroic than many ordinary people were doing every day in real life.
Certainly it would be farcical to have (for instance) Simon breaking into the Berghof and punching Hitler on the nose. Even so, it seems bizarre that a skilled pilot who can pass for German (as he does in Getaway) should be spending his time trying to get attention for a formula for artificial rubber, as he does here*.
Charteris's writing never falls below a certain minimum level of competence, and the villains don't quite descend to the "Ve haff vays of making you talk" level, but this is just plain dull.
P.S. For a list of — and discussion of — all Charteris's Saint books, see my So You'd Like To... Guide.
*Indeed, in a couple of post-war stories (e.g. "The Covetous Headsman") there are passing references (no more) to wartime exploits in Europe.