I have been asked to tally the various theories about what happened at Lake's camp, in the interest of fairness, even if Rachel thinks them ludicrous. Here, then, are all the theories I have heard discussed, ranging from least to greatest on the Betsy Scale of Sensibleness (or greatest to least on the Rachel Scale of Exciting Plotting):

1) THE PENTAFORMS DID IT!

The Pentaforms killed off the humans and left. Dyer's manuscript is probably reasonably accurate, unless the Germans edited it for their own purposes. The Germans and Lexington might be motivated either by advance knowledge of events (which we might still not yet have) or human curiosity, or both.

A secretive group of humans, possibly sponsored by some government, has been living in the cave system, and killed off Lake's expedition when they got too close. (Example: The Japanese, using technology acquired from a survivor of the little-known Gray Dragon Island debacle, are conducting underground nuclear tests out of sight of the prying eyes of the rest of the world.) This is not as ludicrous as it sounds at first - the temperature underground stays at about 55 degrees if you hit a certain depth, no matter where on earth you are, a fact often exploited for survival in Siberia. The Germans have got wind of this, and have come to investigate. They probably suspect we know something about it, too. The Dyer manuscript is either a fake to throw us off the scent, or a largely true document irrelevant to anyone except scientists, or a true account with bearing on what the underground agency is really doing, given to us by the Germans in the hope that we would tell them what we knew, in turn.

The secret German expedition killed off the Lake camp in 1930, and are back to make sure we don't find out whatever the secret is. The 1930 Germans had forknowledge of whatever is actually important down here, either from a previous expedition or from the final chapters of the Pym text or some such, and decided it must belong to Germany and Germany alone (a fortune in oil, perhaps, such as is frequently found near huge fossil caches? Oil is, after all, ancient organic matter . . .) The Dyer manuscript is either a blatant fake to entice small groups of us over the mountains in the company of Germans, where we can be disposed of more easily, or (if the city exists) a partially true account meant to throw us off the real scent.

The Pentaforms, when warmed, release a hallucinogenic gas. This is what upsets the dogs, with their keener sense of smell. The gas eventually drove most of the Lake camp mad, and they killed each other off. When the Dyer team came to investigate, they looked at the fragmented pentaform parts first thing, according to his document, and they started hallucinating as well. The events in the city of the mountain are either a complete hallucination or a partial one inspired by an actual ancient city, although a completely dead one. We have not been affected in only a minor way, because we have elected to keep the Pentaforms cold. The only time we warmed one, Betsy thought she saw it move - a hallucination, perhaps, with worse ones only just barely nipped in the bud?