I'm gonna go with the usual option of cross overs involving teleporting police boxes.
A wierd humming/hissing sound sounds through the corridors of the Astartes field command.
In response to these strange noises a Space Marine is sent to investigate.
He see's the Tardis and walks towards it, bolter held at the ready, when all of a sudden a humanoid opens the door and jumps out.
He speaks, "ah the forty first millenium, I wished we didn't come here, the death and destruction is terrible and the Space Marines, ah they are silly little people, whorshiping the Corpse Emperor, I still can't believe they don't know the Emperor is the Face of Bo."
The Space Marine raises his bolter at the humanoids head and yells, 'You speak heresy.'
"No my dear Astartes I speak the tru..."
his sentence is cut off by a burst of Bolter fire that kills the doctor instantly, even regeneration can't save you against a bolter to the face.
Then the Space Marine throws a Frag Grenade into the Tardis while muttering a prayer of piety to the God-Emperor.
After the grenade goes off he runs inside to find a humanoid on the floor with blood seeping out of a leg wound.
'Taste retribution Heretic scum!' The Space Marine screams as he empties his clip into the Companions face.
I think you get my drift.
