Kids with blue lights in their fingers. Oh, and they're dead. Maybe.

[oddhero]

Yes, that description is about as coherent as it gets. I read this book in the late 70s or early 80s in the UK (it was a library book: maybe not relevant but all details helps). There were two kids who were recruited by a man with a military sounding title ("captain" comes to mind) and the signal they were going to join him was a blue light inside the back of their hands/knuckles. Now, I was reading so many titles then that I may have mixed and matches accidentally. It stuck in my head as a haunting, cold book, but that's about it... any leads would be appreciated!