How many times have we seen this sort of thing crop up, with people demanding to know who the person is and then the guy comes forward with a perfectly reasonable excuse.
Give him time to respond, if he does let you down THEN seek legal advice. Give the guy a chance before going that far!
E-mail him stating you want an explanation, if no response, name and shame, then do as Gary says, if you feel its nessaccary.
Jordan