I picked up Super Genius Games' A Peculiar Pentad (for Call of Cthulhu - licensed, oh yes) about a month or so ago.  At $15, it was something of a convenience buy, if not an opportunity one.  Weird CoC stuff has a way of going OOP fast (so says my copy of The Unspeakable Oath #1).  It's approx. digest sized, and I read through a good portion of its 57-odd pages while on BART coming back from EndGame. 

The B&W interior reminds me of a bit of Keith Senkowski's Conspiracy of Shadows, but a bit moodier. The contents are as advertised on the back: "A Particular Pentad presents five shops that every investigator may need to visit ..."  The three advertised are a rare book store, a repair shop and a social club.  Each of the five shop's 1920s location is covered in several pages, including CoC stats and a few paragraphs on using each location in the modern and Victorian ages, describing the shop, proprietor, public and less-so wares, and inside secrets.

In addition to the five locations, the book opens with a 9 page section on using the locations in ongoing CoC campaigns, including a sample neighborhood setting for them ("Pentagon Place").  Among the brief, but useful advice is how shops might treat their new patrons, on first visiting, return, and repeated visits, as well as finding the shops in the first place.

Overall, my first impression is that A Peculiar Pentad would make for some great go-to / on-hand material for the CoC keep, or GM of similar games (horror, conspiracy, possibly pulp), especially for the price. Despite the lack of a ToC or index (to be fair, it is brief, and only has five unrelated shops), it seems handy - especially useful in a longer term campaign. The modern and gaslight advice is brief, but appreciated.  A Peculiar Pentad would be likely be less immediately useful for sci-fi / post-modern games (such as CthulhuTech) or fantasy, pre-Victorian.