The CM series of modules isn't really one that you hear to much about today even with the OSR raging on about classic modules. I first encountered CM3 Sabre River in about '85 when I got involved in playing a friend's dad's higher PC level game.
"CM3 Sabre River was written by Douglas Niles and Bruce Nesmith, with a cover by Keith Parkinson"
"What's so important about Frank Mentzer's Dungeons & Dragons Companion set? Well at its heart everything is built around the PC's domains & strongholds;
"The Player's Companion covers information on character levels 15-25. The book begins with commentary on the changes since a character began as an adventurer at level one. It introduces new weapons, armor types, and unarmed combat rules as well as providing details on running a stronghold and its recurrent costs, such as wages of the castle staff. The Player's Companion details the new abilities and increases in skills, spells, and other abilities that accrue to members of each character class as they rise in level. This section concentrates wholly on human characters, treating dwarves, elves, and halflings separately. The concept of "attack rank" is introduced for the three demi-human classes; although, per the Expert Set rules, they are capped at a specified maximum level. Further accumulation of experience points increases their combat abilities. It also introduces the optional character class of druid, presented as a special progression for clerics of neutral alignment"
We've seen the role that Norwald plays in B10 Night's Dark Terrors but its really in B12 Queen's Harvest by Carl Sargent that sets up everything for the politics of Frank Mentzer's Dungeons & Dragons Companion set! Yup that's right the steps, rules, etc. are all there in the second part of B11 King's Festival.
The Dungeons & Dragons companion set takes the PC's from being middling of the road adventurers straight onto the path of being eventual royals themselves. Don't worry you don't need to grab the Dungeons & Dragons companion box set because all of these rules & such are in the Dungeons & Dragons rules Cyclopedia.
CM3 Sabre River introduces a monster that will haunt my dreams, the sabre claw. A humanoid demon like creature which a flock of which can dispatch even high level parties of PC's. Back in '85 we had half of our seven player's PC's slaughtered by these winged horrors. These monsters were only ever featured in the Creature Catalog & CM3. There are reasons for this. They are monsters that can cause havoc for small parties of adventurers.
But is CM3 Sabre River a good module? I happen to think so because in many ways it helps to fill out another very weird & slightly terrifying corner of Mystara. The whole module has the vibe of a thriller movie where your not quite sure where the next issue is going to come from. The fact is another plus is the way everything is laid at the dungeon master's feet. The whole of CM3 is placed on the shoulders of the players & from their its sink or swim.