Oxnard, Calif.�Mark O. Hiepler is as high as a plaintiffs’ attorney can get in this coastal town. He practices on the 15th floor of one of the two high-rises in a community known for sprawling farms.

From his perch, 55 miles north of Los Angeles, the 36-year-old lawyer takes health maintenance organizations and their doctors to task in a practice whose profile is high enough to land him on front pages and TV screens.