Where are you located? Do cucumbers normally keep growing lustily in late October where you are?

The puckering and cupping of leaf tissue looks a lot like what you'd expect from Cucumber Mosaic virus. There are CMV resistant varieties. Aphids are the vector. It can be transmitted to other plants, so best to get rid of them.

https://aggie-horticulture.tamu.edu/vegetable/problem-solvers/cucurbit-problem-solver/leaf-disorders/cucumber-mosaic/

Aaarrrgggg. That’s what I was afraid of. I’m actually in San Antonio, Texas and this is the first time I’ve ever tried to grow anything. My parents live a bit south of me and have been very helpful with suggestions. (I come from a long line of Aggies, so I’ve got lots of advice!)

I think if we plant them in mid-September, as long as we can get some “good growth,” we should be able to have some cucumbers before the first frost.

Not sure if that’s true, though.

So I should probably dig this plant up? It’s growing next to two tomato plants that seem to be doing quite well, with no signs of Aphids.

Well, you're not going to cure it, and it poses a risk to other plants, so digging it up and disposing of it (DO NOT compost) might be wise. I've always been skeptical about late summer planting of summer veggies in this climate, but some people swear by it. I assume this was not a CMV resistant variety. Might go for that next year. Early season aphid control might be smart as well.

Thank you so much, Dan! That’s exactly the information I was looking for. And I’ll definitely take your advice about timing when it comes to planting summer veggies.

Thanks again!

Apart from the mosaic pattern I see dark specks as though it is full of bugs.