So, the first half of the show got taken over by rabbits.  We're not sure how it happened, maybe somebody left the door to the hutch unlocked, but we had to do an awful lot of chasing them down.  The second half of the show is all about time travel by means other than the TARDIS.  We really get in depth into how things work and the difference between time travel in the TARDIS and time travel via Vortex Manipulator.
WARNING: Contains rabbit chasing
Link: Time Travel Simulation Resolves “Grandfather Paradox”