Derek will play a "well-preserved" mother who runs a horse stable where a murder is committed, according to Entertainment Weekly.
Welch will play the matriarch of villain Diego Navarro (Carlos Bernard) and his son Esteban aka "The Miami Taunter" (Kuno Becker), TVLine reports. Her episode will air after Derek's.
Welch, who broke out in One Million Years B.C., last appeared on TV on the short-lived 2008 CBS sitcom Welcome to the Captain. Derek, who is best known for her role in 10, can next be seen on Chuck, where she will play herself.
CSI: Miami airs on Sundays at 10/9c on CBS.
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