Also to appear on the show are previously announced guest stars Wil Wheaton, Felicia Day, Ming-Na and Stan Lee.
Season 4.5 of "Eureka" is to begin on Syfy next year. The exact premiere date has not yet been announced.
"Wallace Shawn will portray Warren Hughes, a relationship auditor sent to Eureka to shadow and report on Jack Carter (played by Colin Ferguson) and Allison Blake (played by Salli Richardson-Whitfield,)" Syfy said in a news release. "Aaron Douglas appears as Ray, the exuberant leader of 'Galaxy Camp.' And Dave Foley will appear in the season 4.5 finale as Drew Plotkin, a former weapons specialist turned eco-scientist whose research may be wreaking havoc in Eureka."
Eureka is described as a cozy, Pacific Northwest town, which serves as home to a secret community of geniuses assembled by the government to conduct top-secret research, the cable network said in a synopsis.
The show has been renewed for a fifth season.
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