Two CD Grimes Mysteries. The final two books of the series are more of the action adventure form, though not to the popular extremes.
Deadly Island, one of the "kids" is charged with murder on St. Whartons. CD goes there to see what is really going on. He finds a situation where some world criminal leaders are plotting to take over South America through economic manipulation.
A Step Too Far, Shirley's sister is murdered. It seems to somehow be directed at CD. He can't figure who or why - at first. When he finds out, he has to try to stop some old foes in prison who are manipulating people into doing their dirty work for them.