Tomorrow Is Yesterday
The Enterprise gets back to its own time, and Kirk checks in with Starfleet Command.
Spock (to Kirk as he signs off with Starfleet): "Excuse me, Sir, I just found something else I missed in my original review of the historical records."
Kirk: "You did, Spock? What was it?"
Spock: "Captain Christopher had a second son, Jeffrey Sean Christopher..."
Kirk: "OK, but why did you go out of your way to tell me this?"
Spock: "He was actually Jeffrey Sean Christopher, Esquire. And said gentleman got a hot tip on a new invention--the historical records system. Bought it and patented it. Every time it's used, there's a 5 million credit royalty. And our bill just came in. Sir, Starfleet Accounting won't be happy."
Kirk (on intercom): "Scotty, any chance we might reverse that slingshot we just did?"
End of episode music plays. Cut to commercial.
Here's a very twistwed take of Tomorrow Is Yesterday in general (link)
(And no, I didn't do this one - but I found it one day, really liked it, and thopught a link to it would be appropiate here

