The West Bank.  The first Christmas morning, ever.  An otherwise silent night is interrupted with a loud crack and a brilliant flash.  Suddenly, a flying DeLorean DMC-12 is hovering 1,985 feet above the ground.

Doc Brown: Great Scott, Marty!  What have you done?!

Marty McFly: Relax, Doc!  It was an accident!

Doc Brown:  You set the time circuits to the year ZERO!  Do you know what this means?  Our presence here could unravel the very fabric of the space-time continuum and destroy the entire universe!

Marty:  But it's Christmas!

Doc Brown:  There won't be a Christmas if we stick around much longer!  There might not be any holidays at all!  Hanukah, Kwanzaa and Ramadan could cease to exist as we know it; there won't even be an Arbor Day!  Granted, that's the worst-case scenario.

Marty:  Well, that's a relief.

Doc Brown: In any case, we need to land so we might find fuel for Mr. Fusion.  We MUST return to our own time immediately!

The airborne DeLorean begins to move off towards the nearby town of Bethlehem.  However, Doc has left the headlights on, making the automobile visible to three men and a telephone booth some miles off.

Rufus:  Ah, there it is.  William?  Theodore?  See that star-like glow?  That's where you're heading.

Ted:  But we can't fly, Rufus.

Rufus:  I know, Ted.  You're going to the place underneath it.

Bill:  But why, dude?

Rufus:  I can't really say, amigos.  Just know that the future isn't the only place where you're considered wise men.  Enjoy the first Christmas.

Ted:  The first?  Whoa.

Rufus steps into the phone booth, dials a few numbers and vanishes, leaving only the booth behind.  Meanwhile, Doc Brown and Marty have landed the DeLorean and are approaching a manger.

Marty:  Doc, trust me, I've done this before.  Nobody ever thinks to check barns for time machines.

Doc and Marty bring the DeLorean to the manger's entrance, only to find a speechless and visibly horrified Joseph, Mary and Jesus.

Doc Brown:  Great Scott.

Before anyone has time to react, Bill and Ted walk in.

Bill:  Using the time machine to skip a few days is much easier walking, Ted

Doc Brown:  More time travellers!  We've changed history!  Marty, try not to be noticed!

Marty:  Doc, there's a DeLorean and a phone booth in here!  We've been noticed!

Doc Brown:  Yes, but if we do anything else, we might bring more unwelcome visitors from the future!

Bill and Ted are oblivious to the conversation between Doc and Marty

Ted:  Billy, I just realized something.

Bill:  What is it, Ted?

Ted:  Rufus said it's Christmas and that we're wise dudes, right?  Well, doesn't that mean that there should be three of us instead of two?

Bill:  You're right!  Okay, go back to the phone booth and get yourself from an hour ago!  Oh yeah, and we're going to need gold, myrrh and Frankenstein!

Ted:  Frankincense, Bill!

Ted leaves.  Moments later, two Teds appear dressed head-to-toe in robes and bearing gifts.  The Teds and Bill all approach Joseph and Mary.

Ted:  These are for your holy dude, holy dudes!

Joseph and Mary are clearly frightened by Bill and the two Keanu Reeves lookalikes, but they accept the gifts anyway.  Suddenly, Max Walker bursts in wielding a pistol.

Mary:  (In Aramaic)  It's one of Herod's men!

Max:  I'm with the Time Enforcement Commission!  None of you time-travelling scum are supposed to be here!  If you don't all leave immediately, all of you will be in violation of TEC Code 40.A!

Doc Brown: I knew it!

Bill:  Teds!  Your dad will send you to the military academy if you're arrested!

Teds:  (Clearly panicked)  Catch ya later, dudes!

Bill and the Teds flee

Doc Brown:  You know, Joseph, I know a guy named Mr. Fusion who could put that myrrh to awful good use.

Doc gestures towards the myrrh

Joseph:  (In Aramaic) Yes, yes, take it.  I don't even know what this stuff is.  Please, just go

An exchange between Doc Brown and Joseph of Nazareth takes place.  Marty becomes perplexed.

Marty:  Hey Doc, what was all that talk about screwing up future events?  The space-time continuum?

Doc Brown:  Well, I figured, what the hell!

Max:  Hey!  Don't swear in front of the Messiah!

Doc Brown:  Sorry.

Epilogue:

Infant Jesus:  (Thinking)  Wait, where am I?  Who are all these people?  What's going on?  Where's Al?

Cut to Joseph adoring one of the two remaining gifts

Joseph:  This gold is so shiny!  I can even see my face in it!  Look Jesus, see the shiny gold?

Jesus looks into the piece of gold Joseph is holding over his head and sees the reflection of Dr. Samuel Beckett.

Jesus:  (Thinking)  Oh boy.

And that's how "Quantum Leap" SHOULD have ended.