The BFI provide a nice overview of the film and its points of interest here. It's basically a detective story with two threads: Inspector Carson of Scotland Yard who is trying to crack a secret ring of people helping Nazi war criminals escape Europe, and Jonathan Blair (Lee), who produces a weekly newspaper cartoon strip based on drawings of a live model named Penny. They are tied together by two things: Carson's secretary and Blair's model are flat-mates, and Blair turns out to be part of the criminal ring, conveying secret messages to the escaping war criminals via the hair-styles which he draws for Penny in the strip.
This means Lee appears in the film in two modes. Early on, while we still believe he is an ordinary comic-strip artist, he is urbane and charming, much in line with what he'd already done in Corridor of Mirrors, and speaks in a light, high voice which I barely recognised as his (even allowing for the imperfect sound-recording technology of the time). But once his true identity is revealed he adopts a harsher, brusquer manner, his voice drops and becomes much more like the one we all recognise, and he literally ends the film wearing a leather trench coat, toting a gun and delivering what I believe to have been his first ever cinematic death scene. He comes across as a little mannered and wooden throughout, but these were early days. Certainly, templates were being laid down. He makes the same transition from apparently-charming to (admittedly much more) ruthless in Dracula, while he would don many another leather trench-coat in later roles as literal or analogous Nazis. It's all very charming to see.
Around him, the film is nicely structured and perfectly competent given its budget, with a few moments of humour and a decent chase scene towards the end, though nothing particularly powerful or profound. It comes pretty close to passing the Bechdel test by dint of having three speaking female characters (Penny, the comic strip model, Molly the Scotland Yard secretary and Mrs Hodgson, Blair's cleaning lady), and including at least four substantial conversations between Penny and Molly over the course of the film. Penny is fascinated by Molly's job and asks lots of questions about it, but because Molly's boss and colleagues and the people they are trying to bring to justice are all men, this means that even a conversation about Molly's working life and both women's aspirations is inherently still about men. Molly herself is played by Diana Dors, in a surprisingly dowdy role given her later image, and not the last time she would co-star with Christopher Lee either.
Not a film I would have watched for its own sake, but a welcome stop on my ongoing tour through Lee's screen career.