It hurts to give any film with Sidney Greenstreet and Peter Lorre less than "5" on a scale of "1" to "10", but BACKGROUND TO DANGER (despite their presence) is not a good World War II espionage piece. It may be the weakest movie ever made from an Eric Ambler novel.
Between 1938 and 1945 Ambler wrote five spy or international crime novels that (with his contemporary, and master, Graham Greene) reshaped the whole genre. Ambler's books were CAUSE FOR ALARM, BACKGROUND TO DANGER, JOUNRNEY INTO FEAR, THE MASK OF DEMETRIOS, and EPITAPH FOR A SPY. The greatest of these was the last that he wrote - THE MASK OF DEMETRIOS (also called A COFFIN FOR DEMETRIOS) which Greenstreet, Lorre, and Zachary Scott turned into one of the best portraits of a totally amoral criminal in cinema. Orson Welles helped direct (and supported Joseph Cotton in) JOURNEY INTO FEAR. I'm not sure by I believe that EPITAPH FOR A SPY (set in France in 1938) and CAUSE FOR ALARM (dealing with economic rivalries between somewhat allied axis countries) were not made into films. Someone may correct me on that.
CAUSE FOR ALARM introduced a Communist Russian agent and his sister to Ambler's readers. Tamara and Nicolai Zarashoff are (when not pursuing espionage for their government in Moscow) bickering all the time. Ambler liked to humanize his characters (such as his masterpiece, Arthur Abdul Simpson, in THE LIGHT OF DAY / "TOPKAPI"), so his villain Demetrios Talat turns out to be a determined social climber, using his talents for evil in THE MASK OF DEMETRIOS to assist a bank, the Eurasian Credit Trust, on which he ends up a director. The Zarashoffs and their unwitting ally in CAUSE FOR ALARM manage to cause a brief split in the interests of Nazi Germany and Fascist Italy in early 1939. One would have known this when reading BACKGROUND TO DANGER a few years later, when they reappeared.
When talking about the film FIVE FINGERS I gave the background of Turkish neutrality in World War II. Ambler tackled this in the novels BACKGROUND TO DANGER and JOUNRNEY INTO FEAR, pointing out that Turkey's police and army were scrupulously looking out to protect that neutrality (Col. Haki, who helps tell the introductory part of the story of Demetrios in THE MASK OF DEMETRIOS - played by Kurt Katch there - reappears as Orson Welles, protecting American engineer Joseph Cotton in JOURNEY INTO FEAR: to make sure Cotton finishes his job in arming Turkish naval craft). In BACKGROUND TO DANGER, Ambler (correctly) shows that German agents were more likely to try to push Turkey into the Axis camp by underhanded means. The villain is the ambiguously named Col. Robinson (Greenstreet, of course) sent to contact those anti-British Turkish nationalists who would join the Germans. The problem is that the novel demonstrated Ambler's tricks with Robinson in a way the film didn't. Robinson is German, and speaks with a German accent (in fact one of the characters says that he could not possibly be English!). Greenstreet had one of the finest English speaking voices in film.
The Zolashoffs are here again (in the novel bickering again) but here working with the American played by George Raft. But in the novel, Raft's American is very naive - and they are educating this new ally in the "background to danger" to Turkish neutrality very quickly. This is not the story as W. R. Burnett made it in his screenplay, making Raft's character an American agent (which he wasn't). I can only guess that he did this to make the no nonsense Raft more believable - who could imagine Raft as a chump?
It doesn't work - the novel is constructed for the Raft character to gradually realize the dangers of the Nazis and their allies, and the fact that (dubious as it is to us) the Communist agents were a better bet for allies. Instead the story makes Raft's character become a typical World War II propaganda hero - he can handle these Nazis with a blindfold on!
There are some nice moments (due to Sidney and Peter). Greenstreet in particular has two nice ones that come to mind: when he notes his favorite set up (a Strauss waltz on a gramophone and a dead body on the floor), and later when his plans have all collapsed, and he is informed he must return to Berlin (his quick look of horror at hearing what will be his death sentence is done very well). But such moments are few and far between. The rest of this film sinks those few moments one recalls with fondness.