Almost certainly my own fault for not phrasing my initial question properly.
I get what the Tempest spell does on paper but if you think of HeroQuest (and many other games) as having a whole “turn” or “round” that consists of individual turns for each figure on the board in sequence, starting with the Heroes … Hero A, Hero B, and so on, then Zargon’s bit which comprises of an individual turn for each monster on the board, Monster A, Monster B and so on, then that whole or complete turn or round basically represents a period of time during which potentially a lot of things happen involving a lot of individuals all mixed together (but for the sake of our sanity and rule simplification we handle it through individual sequenced turns)
If you consider the Tempest spell and more specifically the “miss its next turn” piece in this context then it feels odd, out of place, to me compared to other similar spells in particular and the rules in general, almost like it has been dropped in from a simpler game with more of a “player 1 takes a turn, player 2 takes a turn, player 3 misses his turn, player 1 takes a turn and so on” kind of structure.
If, for example, on Zargon’s turn a Spell Casting Monster casts this spell on the Wizard, it takes effect immediately (presumably?) enveloping the Wizard in a personalised whirlwind rendering him unable to move, attack, cast spells, search, drink a potion? open a door? and yet he can still defend against my next monster when it attacks him, how can it attack him if he is surrounding by a whirlwind, how can he defend, why does he need to, could that monster if suitably armed attack the Wizard with a ranged weapon? What chance does a quarrel have of hitting someone surrounded by a whirlwind? If my crossbow attack results in him losing his last BP, can he use a healing potion or cast a spell to save himself, after all it isn’t his turn so why would he miss it? Once I as Zargon have finished my turn then can the Barbarian move next to the Wizard and pass him an item or a potion or have the Wizard pass him an item?
I’m not expecting an answer to all those questions, just indicating that the way it is written feels like it dates from early in the game’s development and wasn’t ever revisited to reflect other changes that made the game and turn sequence richer, like the interactions between figures, such as passing items and the special save rules introduced in the US version.
Perhaps something like the following would be an improvement in clarity.
“This spell creates a small whirlwind that envelops one figure of your choice. The spell takes effect immediately and lasts until the start of the caster’s next turn. Whilst under the effects of the spell the victim is completely isolated and cannot perform any actions or interactions, including movement, neither can they be affected by the actions or interactions of others.”
This also has the unintended but interesting option of a caster using this spell as a form of last-ditch defence, if surrounded by monsters and running out of BP, a caster could use this on themselves to isolate them for a turn in the hope that the other Heroes can clear the decks in the meantime and the same is true for a Dread caster.