Two sisters . . .
The McKenzie Sisters Mystery Series was created by Samantha St. Claire. Rose and Cassandra (aka Casey) are no ordinary sisters. One is scientifically inclined, lives in Denver, and rides a bicycle like her life—or a case—depends on it. The other rides trains, wields a blade, and keeps her identity as a Pinkerton "under wraps." The sisters also have a knack for solving cases . . . and getting into trouble while doing it.
Each book takes place in a different Colorado location but they happen simultaneously. They are stand-alone novels and can be read in any order.