For murder mysteries I would recommend Ian Rankin's Rebus books, Peter Robinson, Jonathan Kellerman, Faye Kellerman, Stuart McBride, Val Mc Dermaid, Reginald Hill ( Daziel and Pascoe books), Stephen Booth, Michael Connolly, John Connolly, Peter James, Mark Billingham, John Harvey, Ruth Rendall and Henning Mankell.
For medical murder mysteries, try Kathy Reichs and Patricia Cornwell.
For espionage try John Le Carre , Len Deighton( London Game, Mexico Set and Berlin Match), William Boyd and Ken Follett.
For thriller I would recommend Frederick Forsyth, John Grisham.
Ruth Rendall writing as Barbara Vine writes some very interesting twisted tales. Hope all this gets you started on one of the most enjoyable activities of all.