Subject and Verb do not agree. Sequoia and Charles plan to exercise together.
The subject of this sentence is a compound subject (Sequoia and Charles). A compound subject is a plural subject because it has more than one. The verb "plans" agrees with a singular subject because it ends with /s/. In order to make the subject and verb agree, the /s/ at the end of "plans" needs to be eliminated. The revised sentence should be "Sequoia and Charles plan to exercise together."
