gatecrasher vs undercover agent

gatecrasher

noun
  • The groom or one of his groomsmen when partaking in the gatecrashing ritual of a traditional Chinese wedding. 

  • A person who enters some event without a ticket or invitation, either by stealth or by deception. 

undercover agent

How often have the words gatecrasher and undercover agent occurred in a corpus of books? (source: Google Ngram Viewer )