BULLETPROOF TEXAS (4) by Kay Thomas: Scientist Max O'Neil thinks there may be a cure for cancer in the clear waters of a pond recently discovered in an underground cavern. Her pharmaceutical company sends her out there to investigate. But park ranger Zach Douglas' sister was killed by a corrupt pharmaceutical company's renegade enforcer, so he doesn't buy Max's explanation that she's conducting research for women's cosmetics. Then equipment is sabotaged, a student is murdered and rumors of diamonds have desperate townspeople trying to close down the cavern for their own exploration. Thomas' characters are not easy to like, but the unwinding plot is taut, tricky and worth the read.