I think the members who rated this 2 stars want a different kind of mystery. There is no detective here and the central crime isn't murder. The Scarlet Imperial is a jewel-encrusted egg, which we learn is stolen. What we don't know is who stole it and when nor why it is now surfacing. More especially, we don't know which are the good guys and which are the bad guys.
Eliza Williams works for (and loves?) Towner Clay who has placed her as secretary to Bryan Brewer. She doesn't want to be a secretary, but this is what he wants her to do, so she does it. One day while Mr. Brewer is out of the office a man comes in with a white box for Brewer. He leaves it and Liza puts it in the bottom drawer of her desk. Brewer doesn't return that day, but a messenger comes to get the box. Liza is suspicious of this "messenger" and says she doesn't have the box.
Pretty much all goes downhill from there. I thought several times this would make a wonderful old black and white film. This fits the period perfectly, of course, having been originally published in 1946. The characterizations are certainly not fully-fleshed - one should not expect them in this genre - but one can easily see the straight faces with the lies told, but also fear and questioning as appropriate. I thought early on this is probably a very good 3 stars, but I'm bumping it up just because it was such fun to be with Eliza and the others.