It's basically like getting Law & Order episodes in the mail. Each box is an "episode" with a mystery you solve by using puzzles, evidence, interviews, and more as part of the Criminal Investigation Unit on the case. If you choose to subscribe, you'll get more episodes for the first "season" (five episodes in total), at which point you'll get to unlock Season Two.
Promising review: "This was by far the best serial box I have ever done! Good story, easy-to-remember characters, fun puzzles (many kinds and difficulty levels), and the most high quality props and tangible items I've ever gotten--even with boxes I paid a lot more for. Each and every box contains really fun items in it (not just paper). Clues are given in the most original, fun ways! There is also a website which provides hints and solutions so you can get as much, or as little, help as you want--and never a spoiler. I strongly recommend A Killing Affair! it's a bargain at this price. I can't wait for the second series to come out." —Donna D.
Get it from CrateJoy for $44.99 (or as low as $33.99 per month with a subscription).