This objective states, "The keeper wins if a mi-go kills an investigator," and "The investigators win if Helena Detaigne is killed."  As the keeper, I'm at a loss here-- where are the mi-gos?  Am I missing something?  Event 3 spawned Helena Detaigne, allowing the investigators to swarm her and kill her.  And they have 5 turns to do this before event 4 spawns 2 mi-gos!  5 turns is more than enough to kill Helena Detaigne before I can spawn any mi-gos.  I searched through the mythos deck and nothing there spawns mi-gos and no Keeper Action cards can spawn them.  Is event 4 the only thing that gives me mi-gos?  Please help.

Ugh, CC, you're the worst.

There may simply be no other way to get Mi-Gos out.

Isn't Helena out of reach for the investigators in this one until they find Clue 1? She appears early and taunts them from the locked room (Library or somewhere in the Attic) that the investigators can't get to without finding the last Clue. At least, that seems to be my recollection, not sure if that's this Objective or another though.

Yeah, she's in the Library which is locked.

Only time I played CC I played this objective, and I actually managed to kill one of the investigators with my last mi-go (as the other one was killed off).

 Yes, she spawns in the library, which is locked to the investigators, but, like all monsters, she, herself, is not restricted by the lock.  So somewhat foolishily, I took her out to grab samples off the investigators to boost my threat as there were 2 standing in the study, which has an altar right next to the library.  I got my threat, but I never made it back to the library.

I'll be careful not to let her get smacked around if I run 1C.

Especially as the Keeper knows how he and the investigators win (long before the investigators do), seems silly (to put it politely) to send Helena out into th open to be killed. Turtle, turtle, turtle. It's not like there is that much you need Threat for in CC, I think most of mine is always spent on playing and drawing Mythos cards (don't think we've ever run out of Darkness tokens, but then, I don't spam Darkness every turn).