Looks like bugs to me. Take a magnifying glass and look for little black spots that move around on the bottom side of the leaves. (spider mites, possibly?)

Do you spray the leaves with anything? If so...what? Also, if so...stop now.

In a pot with straight compost? Bugs love compost, and it's a terrible potting medium. Can suffocate and burn the roots, or not hold moisture and prevent nutrient uptake. What did the last plant's roots look like? Regardless, if they are in straight compost, you'll need to find some decent potting soil asap. One with perlite for good areation and drainage.

Taking a plant from inside to outside and back is a good way to introduce bugs to your houseplants, and your guests, and pets, and cupboards...(roaches and spiders love to crawl into the drip tray for shelter and food)

Watering your lady is important. Make sure you get moisture to the lower root zones, or it will restrict root growth.

Is that a spider web on the lower part of the leaf?

Might want to check the FAQ section and learn some tips for soil, nutrients, water, ph...
Rusty Trichome Reviewed by Rusty Trichome on . Plant Dying!!! Brown spots Hi I have a young plant which is 4 weeks old and is grown in normals everyday compost in my conservatory which does not normally get very hot, when it does I move it outside. I water it with normal tap water every couple of days making sure the soil is not too wet (with no nutrients), but for some reason the lower leaves have brown spots appearing on them which then consume the whole leaf, and then wilts downwards and dies. This then happens to the leaves above and so on until the plant dies Rating: 5