The Daleks reveal themselves

The Doctor learns that the men who stole the TARDIS (his time machine/spaceship) and transported him and Jamie 100 years into the past were doing so under orders from monsters that they accidentally summoned while trying to invent time travel. The Doctor asks who exactly these monsters are -- and immediately finds out the hard way that they're his worst enemies, the Daleks. His reaction is one of pure dread as he realizes just how dire his situation is.

Example of:
Oh, Crap!