The Invisible Man is both an action and a comedy (though the series pilot was far more comedy oriented than the rest of the series), with plenty of buddy-cop elements.
Episodes were generally of two types. Many dealt with cases given to Fawkes and Hobbs by The Agency. These usually dealt with assassinations or government experiments that had run amok. During the second season, The Agency was given a nemesis agency called Chrysalis which was usually behind that week's conspiracy.
Alternatively, episodes dealt with Fawkes' quest to remove the gland from his head and reduce his dependency on the counter-agent. His unorthodox methods included reviving the mind of his dead brother and periodically contacting Arnaud DeFehrn, one of the gland's creators, though these encounters usually ended with one of the two in pain. The agency considered the gland too great an asset to remove so Fawkes' personal quest usually brought him head to head with those in power.
Episodes usually began with a voice-over with Fawkes who would begin with a quote, usually from a famous person, and commentary about what he was currently thinking. The voice over would reemerge at the end of the episode to sum up Fawkes' opinion on the mission or allow him to voice lingering questions.