Stealthy Steps by Vikki Kestell

Gemma Keyes is an ordinary, unexceptional young woman with a lackluster life until an overheard conversation ends her budding career –
and her loyalty to an old friend puts her very existence in jeopardy. As the truth emerges, Gemma discovers – the hard way –
that invisibility comes with its own set of problems.

Publisher Description

My name is Gemma Keyes. Other than my name, I am utterly forgettable – so those who never paid much attention to me in the first place haven’t exactly noticed that I’ve disappeared. Vanished. Oh, it’s much more complicated than it sounds. And let me tell you, the adjustment is difficult.

I should tell you about Dr. Daniel Bickel, world-renowned nanophysicist. We used to work together, but I’ll be candid with you: He’s supposed to be dead. Well, he’s not. (Imagine my surprise.) Instead of the proverbial six feet under, he’s subsisting in an abandoned devolution cavern beneath the old Manzano Weapons Storage Facility on Kirtland Air Force Base here in Albuquerque.