1977’s The Rains of Eridan is a standalone young-adult hard SF novel by H. M. Hoover.
The Aurora Corporation thought the life-bearing world Eridan promising enough that it funded three bases:
Base One, the administration and living colony research centre;
Base Two, the agricultural research base;
Base Three, the science base.
The bases are separated by hundreds of kilometres, far enough that even if one base were to fall to calamity, the other two would be spared. It seems that the spread was not great enough; bizarre collective madness has attacked all three bases.
Theodora “Theo” Leslie, who has spent the last month out in the field gathering data on the Eridan lifeforms, has no idea how bad matters have become. Not until she witnesses a double murder.