In the episode, the alien time traveller the Doctor (Matt Smith) takes his companions Amy Pond (Karen Gillan) and her husband Rory (Arthur Darvill) to the planet Apalapucia for a holiday, but they find that the planet is on quarantine as the two-hearted natives are susceptible to a deadly plague.
The episode was filmed on a lower budget, and MacRae decided to make the main sets all white in colour.
The Handbot explains the plague and, failing to recognise the Doctor or Rory as alien, attempts to administer medicine that is fatal to them.
Rory explores the complex, and finds an older and bitter Amy, who has been waiting to be rescued for 36 years while hiding from the Handbots.
The Doctor realises they have mistakenly latched onto the wrong time stream, and urges the older Amy to help find her younger self.
[5] Executive producer Beth Willis insisted that Amy's speech about how Rory was the most beautiful man she had ever met make it into the final version.
[3] Gillan developed different body-language, vocal range and attitude for the new individual, whose character has changed after being left behind and in danger.
Dan Martin of The Guardian said that it contained "the series' most tearjerking suckerpunch so far" and the "psychedelic premise [gave] the characters the chance to shine".
He thought the older Amy's "technical wizardry seemed a tad unlikely" (she manages to scrounge up a sonic screwdriver while waiting for the Doctor) but "the power of Gillan's performance skated over any minor quibbles".
[18] IGN's Matt Risley rated the episode 8.5 out of 10, praising MacRae for straying away from a complicated time travel narrative and instead give "a simple yet refreshingly new examination of Amy Pond".
[19] SFX magazine reviewer Nick Setchfield awarded "The Girl Who Waited" five out of five stars, praising Hurran as well as the performance of the three leads.
[20] Patrick Mulkern of Radio Times praised MacRae's dialogue because "it works so beautifully and is delivered to perfection by Karen Gillan and Arthur Darvill".
He also commented on Gillan's make-up job for the older Amy, which "is brilliant in its subtlety" but wished her hair could have been "chopped or grey".
He praised the early scene where Amy was abandoned for the "zingy dialogue" but found himself "enjoying the cleverness of the explanation without really buying into it".
He expressed confusion at how the time-shift worked and thought the problem was too thin to carry out the whole episode, and that Amy's abandonment and love for Rory which was left "[didn't] pull it off".