Destroyer Angel

Anna Pigeon, a ranger for the U.S. Park Services, sets off on vacation—an autumn canoe trip in the to the Iron Range in upstate Minnesota. With Anna is her friend Heath, a paraplegic; Heath's fifteen-year-old daughter, Elizabeth; Leah, a wealthy designer of outdoor equipment; and her daughter, Katie, who is thirteen. For Heath and Leah, this is a shakedown cruise to test a new cutting edge line of camping equipment. The equipment, designed by Leah, will make camping and canoeing more accessible to disabled outdoorsmen.
On their second night out, Anna goes off on her own for a solo evening float on the Fox River. When she comes back, she finds that four thugs, armed with rifles, pistols, and knives, have taken the two women and their teenaged daughters captive. With limited resources and no access to the outside world, Anna has only two days to rescue them before her friends are either killed or flown out of the country, in Destroyer Angel by Nevada Barr.