Older Umbreen

Yasmin Khan is in her family's flat with her family, celebrating the birthday of her grandmother Umbreen. Umbreen provides each of her granddaughters with a gift - she gives a photo of herself and their grandfather to Sonya, while Yasmin is given a broken watch, warning her never to fix it but refuses to reveal why. Curious over its origins Yasmin decides to ask The Doctor to take her back to her grandmother's past so as to see what she was like in her younger days.

In the TARDIS all that Yasmin can tell The Doctor is that Umbreen was in the Pakistani city of Lahore in the 1950s. The Doctor at first refuses to take Yasmin back in time to see her grandmother, as it risks wiping herself out of existence. But Yasmin begs The Doctor, showing her the broken watch that Umbreen had given her. Although still hesitant The Doctor relents and takes the watch from Yasmin and attaches it to the TARDIS’ telepathic circuits, allowing them to find the exact moment that it was broken in Umbreen's timeline.

Much to Yasmin’s surprise the TARDIS arrives in the Punjabi countryside instead of Lahore, confusing her, The Doctor and also her fellow travelling companions, Graham O'Brien and Ryan Sinclair. The Doctor takes out her sonic screwdriver and starts to get TARDIS readings from all around the area. Suddenly, they are struck by some sort of vision of dark figures, and stumble into a road. There they meet Prem, who is driving an ox-pulled cart. They claim to be family friends, and get a ride to see Umbreen.

The Doctor is Attacked

Upon arriving at Umbreen’s home, Yasmin learns that the watch's previous owner is Prem, a Hindu man whom the younger Umbreen is set to marry despite Yasmin's family having Muslim roots. The Doctor notes that the group have arrived on the 14th August 1947, the day before the deadly partition of India.

The Doctor advises Prem and Umbreen to carry out their wedding ceremony soon before they are caught up in the partitioning. However, just before reaching the ceremony, The Doctor again has visions of two alien figures while experiencing brief head pains. They then discover that the ceremony's sadhu, Bhakti, has been murdered apparently by the two aliens. Assuming the aliens killed Bhakti, The Doctor eventually finds their spaceship hidden in the forest. The Doctor at first is unable to get any readings but eventually she manages to identify the spaceship as being a Thijarian Hive and she reveals that the Thijarians are assassins.

Younger Umbreen

Prem claims to have seen them before, standing over the body of his older brother, Kunal while they were both serving in the Second World War. Then the Thijarians appear and they are forced to evacuate the hive. Back out in the forest, Ryan and Prem are transported away appearing some distance away. Not knowing what has just happened all that Ryan can recall is The Doctor telling them to get out of the forest and so they both run. Back near the Thijarians’ spaceship The Doctor notices a device on a tree nearby, a transmat lock, and confiscates it. As she makes her own way out of the forest The Doctor continues to find more locks.

Back at the farm, Yasmin is confused about Umbreen intending to marry Prem. Graham tries to comfort her when they hear Ryan yelling and rush outside to discover what is wrong. The Doctor arrives soon after and tells them to all run for the barn. The Thijarians then arrive threatening everyone there with death, but The Doctor drives them away with the transmat locks. The Doctor then gets them all to source things from around the farm so that she can make some ‘demon repellent’. Later Umbreen speaks with The Doctor, asking her to officiate the wedding, as a doctor is a respectable position, which The Doctor agrees to do. Elsewhere, Ryan, Graham, Prem, and Manish are playing cards. Manish appears to be winning. However, he argues with his brother as he does not want Prem to go through with the wedding.

Now alone in the barn The Doctor, while studying some material that she recovered from the Thijarians’ spaceship, finds herself transmatted back to the Hive. There she learns that the Thijarian world was destroyed in the assassin's absence. They claim to have become witnesses, and have spent 100 generations honouring their lost world. Now they have travelled to Earth to witness and honour those left dead, unseen and unknown, in the wake of the Partition. They then reveal that Prem will become a casualty of the partition before allowing The Doctor to view a recording of Bhakti's death. The footage reveals Bhakti was murdered by Prem's younger brother Manish.

The Two Brothers

Returning to the others, The Doctor reveals what she has learnt - that Prem must die and that the Thijarians are not actually assassins but merely observers to those who are killed. She warns them that they cannot interfere, or Umbreen will never become Yasmin's grandmother. Yasmin however, convinces The Doctor to remain rather than leave, leading The Doctor to perform the marriage ceremony the following day.

After the wedding ceremony Umbreen offers Manish reconciliation, and Manish coldly casts her and his own brother aside. After that, Prem offers Umbreen his watch, but drops it on the ground, where it breaks. Umbreen's mother says the day is truly cursed, but Umbreen says it is instead perfect, and that the watch is theirs forever, their own moment in time. The Doctor then confronts Manish for murdering Bhakti, causing Manish to reveal that he has contacted a group of armed Hindu nationalists to attack the wedding reception. Realising that Manish has betrayed his whole family, as well as murdering the holy man, The Doctor learns that men on horseback are at this moment charging down the road to take their land and so none of them are safe.

Back in the farmhouse The Doctor warns Prem and Umbreen that they all need to leave straightaway. However, as The Doctor expected, Prem offers to stay behind and distract the groups of thugs so that they can all escape. He tells The Doctor to go as well, claiming that he must face these demons alone. And so while Umbreen and her mother escape with The Doctor's group, Prem goes to meet his brother and the thugs and attempts to reason with them but dies when one of the thugs shoots him. As everyone flees the Thijarians stand vigil, honouring Prem.

Back in the TARDIS, Yasmin worries if Umbreen managed to escape or if she will be killed after all. The Doctor tells a relieved Yasmin that her grandmother did manage to survive and will eventually end up in Sheffield.