This post contains spoilers for the latest episode, 5.03, Victory to the Daleks.

To begin: zuh?

In the latest episode, which I just watched, the Doctor is given a choice between destroying the Daleks once and for all and saving Earth from a huge bomb. He calls off the attack on the Daleks and returns to Earth to stop the bomb, which he knows the Daleks are going to detonate anyway.

So, um. The obvious question. If he knew he was going to have to stop the bomb anyway, why didn't he let the attack continue as he went back to Earth to stop it? Also, the bomb had like a two-minute charge time, their whole ship could have been destroyed by then (the Daleks obviously thought they could be destroyed before they could time-jump away). Even if the bomb countdown would have continued after the Daleks were pulverized, well ... the Doctor was planning on having to stop the bomb anyway. Which he did. While letting the Daleks get away to rebuild their empire, dedicated to the destruction of all other species in existence.

Zuh?

I understand the Daleks have to escape to come back as a threat again (as they always do), but couldn't the plot mechanism for the Doctor's choice have been set up a little more believably?