Like a fleet of provoked Daleks screeching in a clamourous chorus of exterminates, devout Whovians greedily snatch at the latest morsel of Series 9 news being disseminated via the trusty Internet -- just those few words to nimble on during long, cold nights of anticipation. Although many of the Doctor's upcoming adventures are still shrouded in a veil of ambiguity, one thing is for certain: a slew of two-part installments is in store for the illustrious Time Lord. And with two-parters, cliffhangers inevitably follow. You never know whether the Doctor's nightmare will truly end, or if that unsatisfactory, grim "until next time" will materialise amid the pending calamity unfolding on your screen. Will the Doctor and his cohorts survive this inescapable doom? Meh, probably. But you can never rest fully assured of their preeminent victory. An eternal week of discontentment and inauspicious forecasting awaits you. In retrospect, two-parters can either be an asset or an utter disappointment within the realm of Doctor Who. Some are only fillers, haphazard spectacles of tangled plot threads stretched out for an additional 45 minutes -- 45 dreadful, cringe-inducing, superfluous minutes. Others are crafted with precision and foresight, extended simply because the writer can't communicate a convincing exposition, climax, and resolution within the span of a standard episode. With Series 9 just around the corner, we can only hope for the latter. In the mean time, here are five two-part stories (excluding series openings and finales) that set an ambitious precedent for the Scottish Time Lord's forthcoming exploits. Let's see if the Doctor can outmatch himself.