So the house was "gutted" by someone else? Then they replaced plaster with plaster? And now everything is cracking--and when it's not cracking it's wet to boot?

All of the renovations were done by someone else right before we purchased the house. We weren't involved in the renovations.

Some of the plaster has been replaced with drywall. However all of the exterior walls still have plaster.

It's cracking in lots of places throughout the house; however there are only two spots that look like they are being caused by moisture. One above the fireplace and the other is above a window in a bedroom

Start checking the roof and outside of the house for water entry points.

Our 1918 house has brick walls, no insulation, single pane windows, original plaster AND... no cracks.

As brickeyee suggests, check for water.

Ditto on checking the roof, particularly the chimney flashing. Most of the damage sounds water related.

Depending on how bad the cracking is, it could be from many causes. My bet is that the renovation covered up lots of surface defects with patching and heavy coats of paint. Now the real surface is coming through. Other causes could be structural changes the prior renovators undertook, normal or abnormal settlement, or simply repainting the plaster in a lighter colour that highlights the natural imperfections.

Are you sure no insulation was added to the exterior walls during renovation? The symptoms suggest added insulation with no vapor barrier on the warm side to me. It doesn't seem likely that water infiltration from exterior leakage would have shown up in so many different places and forms.

This is a serious matter and deserves the attention of a professional even if it is just a home inspector or a local contractor. I would be especially interested in the installation details of the new windows.

its a water damage and its a serious matter cause it can damage the whole property. just check that there is any leakage? if it is so then fix it. and do consult with an expert or water damage restoration company, which can provide all the needed services.
if there is moisture then it can grow moulds. moulds are a kind of fungus and are bad for health.
try to sort out this problem ASAP.

Good Luck!

sherllin

Here is a link that might be useful: Flood Damage Repair

"if there is moisture then it can grow moulds. "

Can you use the moulds for Jello?

Mold.

The water damage companies are not all the useful for this type of work.

They deal with flooding and major leak damage, not slow damage from outside the building envelope.