A cliffhanger is a standard device of serial fiction. It involves the heightening of dramatic tension at the end of an episode to such a degree that the viewer is made anxious about the fates of the protagonists. This, the producers of the work hope, will inspire viewers to return for the next episode, so that they can see how - or if - the protagonists survived.
Cliffhangers were included at the end of almost every episode of the 1963 version of Doctor Who. Most typically, the only episode free of cliffhangers was the last one in a serial, although there were periods - such as most of the 1960s and season 19 - where even these episodes had at least mild cliffhangers.
The device is still used in the BBC Wales version of the show for multi-episode storylines. A cliffhanger has also been a feature of the the last episode of the first three series, in which it served to point to that year's Christmas special.
Cliffhangers are less prominent parts of earlier Torchwood narratives, although each episode of Children of Earth and Miracle Day used them. Conversely, The Sarah Jane Adventures regularly employs cliffhangers, in a style that directly echoes so-called "classic" Doctor Who. SJA stories universally have cliffhangers between parts one and two. Series-ending cliffhangers are much less common in the spin-off series. Only the Torchwood series 1 finale ends in a cliffhanger that is directly resolved in a later episode (though series 4 has an as-yet unresolved cliffhanger). Unusually, this cliffhanger resolves in both TV: Utopia, and TV: Kiss Kiss, Bang Bang, and it is not strictly necessary to have seen Utopia to understand its Torchwood resolution.
As documentary subject Edit
The quality of various cliffhangers - in terms of their efficacy to make viewers return the next week - was the subject of a short documentary, Now, Get Out of That, on the Terror of the Vervoids DVD.