Triple Threat Purity in Death by J. D. Robb Penquin Group USA, 2002, 368 pp, $7.98 Origin in Death by J. D. Robb Penquin Group USA, 2006, 384 pp, $7.98 Fantasy in Death by J. D. Robb Penquin Group USA, 2010, 368 pp, $7.98 Science fiction is not precisely a closed shop, but it does closely resemble a club. Newcomers are measured by how well they adhere to certain conventions. On the one hand, readers cherish novelty, the “what if” factor and the “gee whiz” moment. We love to be dazzled. On the other hand, we tend to be a…