What's the Name of That Book??? discussion

I read this book a number of years ago, so i hope i have the facts correct. This is a 2-book set. Book one is about a husband & wife who descend into tunnels deep below the surface, and then their struggle to return.

I remember more details of the second book: The second book starts with him returning to the tunnels, and his wife goes after him. Many from the surface are "summoned" underground, and this starts a war between the people of the surface and those underground.

The military sets up camps underground, and small towns are established underground as well -- mining, etc.

The wife leads an expedition deep into the tunnels; there are a number of points along the expedition that group is resupplied from above by drilling holes into the earth & dropping the supplies. They encounter the enemy below along the way, and their numbers are slowly depleted. They come upon a large, dark ocean beneath the surface that they must cross, and encounter creatures from the deep.

She & her team ultimately meet the enemy head on and a battle ensues.

Concurrently there is another story between the husband & the leader of the underground people.

There are some vivd details of the tunnels the creatures must crawl through -- some very tight & winding tunnels, takes days to crawl through, sometimes getting stuck and unable to back out.

The Descent?

Sounds a lot like it. Was there body modification/ scarification with the underground people? If so, and it was pretty intense, this is probably the right book.

And there's three of them now :)

That is it!! Author Jeff Long. Looking forward to read the third. Thanks.