“The Wrong Stuff” is a much needed departure from the tension and is a fun, entertaining, and Castle-esque episode. When a case arises involving Major Tom Richwood (Yves Bright), a murdered astronaut on a “Mars 2018” space simulation, the only way Beckett, Castle, and Esposito (Jon Huertas) are allowed to question the other astronauts is to don space suits. While Castle thinks this is “the best case ever,” Ryan (Seamus Dever) isn’t as enthusiastic about stepping onto Mars, fake or not, so he stays behind in the command center to conduct other aspects of the investigation.