Hey, I'm just about to run this series!
I
suppose you could run book 6 as a stand alone - probably with a great deal of effort/re-write/etc.
(Note: I've only skimmed book 3-6 for the overall view of the whole story atm as I've still got a few weeks.
).
In a nutshell:
In PF, every 100 years Baba Yaga returns to Golarian and takes the current witch-queen of Irissen away with her in the Dancing Hut, feeding off of the deposed queens power. (of course few queens have any idea what fate is going to befall them....)
She installs a new queen & repeats the process 100 years later. This has been going on for 14 cycles.
The current queen though has suspicions & no desire to abdicate her throne. She forms a plan to take down Baba Yaga & cover the entire world in endless winter. And is in the process of succeeding. Enter the heroes.
They have to steal the Dancing Hut & take it on a journey that spans continents, planets, & planes/time to rescue Baba Yaga.
Book 1 - the heroes become involved & are tasked by one of Baba Yagas minions to reach the Dancing Hut & use it to track down and rescue her. Book 1 ends with the PCs closing the portal that's spewing unnatural winter into their homeland.
Book 2 - is a trek across the frozen country of Irrissen to hijack the Dancing Hut from the winter witches!
Book 3 - The PCs backtrack B.Y to the country of Ioboria (sp?), fight centaurs, frost giants, explore a dungeon & gather clues & keys to get them to their next stop - a different planet in the PF solar system!
Book 4 - The PCs land on the winter planet Triaxus & need to retrieve 2 clues/keys - from opposing sides in a war.
Evil white dragons! Kinda elf-like aliens riding dragon-like mounts!
Book 5 - Rasputin Must Die!
What a great title! The trail leads to WWI era RUSSIA! Yes, on our Earth. The PCs fight gun toting Russian soldiers, animated WWI tanks (including the real & very bizzare looking Tsar Tank {seriously, google the thing! I can't wait to build one!) & the mad monk himself - Rasputin.
Yeah, I gotta run this!
Book 6 you already know.
The whole point of this series is to go on a cosmic joy-ride in the Dancing Hut. Encountering various winter themed & Russian{?} myth based stuff along the way. And telling a PF story in the process....
Personally I think if you just skipped over vol.1-5 you'd lose a great deal. You'll still have some neat fights though.
If you want a high lv stand alone, try
The Witch War Legacy. It's a one-shot PF module for lv 17 (though I'm sure you can scale it down to lv.13 or so like I did)
It too concerns Baba Yaga, & the plots of the current witch-queen of Irrissen. The queen & a # of rivals (a demon lord + the PCs) are trying to seize a different artifact. The queen in order to further her plans that are revealed in Reign of Winter, the demon because part of him is bound to the thing, & the PCs for any reason you like (self interest or as agents of either of the others).
Very cool dungeon/setting/backstory.
It also serves as a great prologue for Reign.
What I did was run it as a one-shot for our 13th lv, mythic characters a few weeks ago. {knowing full well that when I take over full time DM duties in a month I'm planning to run Reign of Winter
)
My players failed to stop the Witch Queen from seizing the artifact. They weren't concerned though as this was just a one-shot to fill in a week or two play gap.
They have no idea that their failure is going to be very very important to their brand new 1st lv characters....