Anne McCaffrey & Elizabeth Ann Scarborough 
Powers That Be 

It was a world of ice and snow – a planet that just supported life and that had been terraformed from frozen uninhabitable rock.The people of Petaybee were hardy, self-reliant, friendly – and also very secretive.
Major Yana Maddock, medically discharged from the service, was shipped to Petaybee in the hope that her burnt-out lungs might just recover in the icy air.And at the last moment, she was given a special commission.Unauthorized life-forms had been seen on the planet and, more seriously, geologic survey teams had vanished into nowhere, the odd survivor being discovered abandoned and insane.It was Yana“s task to infiltrate Petaybee society and find out who – or what – was causing the eerie events on the planet.
She discovered a primitive ice-bound community of extraordinary people – people who possessed some mysterious quality of surviving – and people who Yana discovered she both liked and revered as she found herself becoming one of them.