Roots: It's a Wonderful Life, Groundhog Day (repeating events, Puxatawnee). Back to the Future. Star Wars IV ('You're our only hope', 'This is our new hope') Mel refers to Edger Allan Poe, Doris Day, Lowery, Theseus and Bing Crosby. Capra sings varients of 'God Rest Ye Merry Gentlemen' and 'Good King Wenceslas'. The word Slithergee is not too dissimilar to Harry Potter's Slitherin - and there is a character called Potter! 1984 (Hate crimes)

Intertextuality: Could the casting of one-time Time Lord and stage Doctor Who Trevor Martin as the inventor of a time machine be more than a coincidence?

Goofs: An unavoidable consequence of this storyline is that the 'wrong' Doctor and Mel return to the 'wrong' adventure on the Pinto - the one experienced by their counterparts and vice versa!

Dialogue Triumphs: "Computers and flashing lights, this must be it."

"He said he'd killed us. I take offence at that sort of thing."

"The city?" "You're getting warmer. In fact, we both are."

Dialogue Disasters: "I want you to give me my Christmas present."

Continuity: In 3060, the Slithergees came to the planet Puxatornee and demanded to be given a moon to live on.

In one timeline:

President Mary Bailey was killed, seemingly by her secretary Clarence, who was made out (by evidence planted by Mitchell) to be an agent of the Slithergees. This caused the rest of the population to rise up and fight the Slithergees, who responded by nuking the planet, leaving it irradiated.

Christmas Day was renamed as Retribution Day in her honour.

Thirty years later, Professor Capra built a time machine (that used leptonite crystals) to allow Lieutenants Stewart and Reed to back in time to change history by killing Clarence before he could kill President Bailey and forcing her to make peace with the Slithergees.

Due to limited supplies, only some important people were allowed food, the withholding of rations from others (such as families) was known as 'rationalisation'. Vape guns (some sort of disintegrator) are in use by the military. The Doctor says they're not good for the ozone layer.

The planet was destroyed when Capra's time machine overloaded.

In one timeline:

President Bailey survived an 'assassination attempt' by her lover Clarence, and gave in to the Slithergees' demands. She continued to do so until thirty years later they pretty much had the run on the planet. Humans were used as sight guides for the Slithergees, and anyone who spoke up against the Slithergees were prosecuted for 'hate crimes'. President Bailey was killed by her assistant Mitchell, who was then killed by the Slithergees.

Capra developed a 'mind peeler' machine to interrogate people, and which was based on leptonite crystals.

The Promixa Century All Blacks did the double in 3012. Pratifoon Wabster had their first number one in the year 3012.

Puxatawnee is the only planet in the galaxy on which leptonite crystals can be found. Quarks, who had taken over the space yacht Pinto, tend to explode in the presence of leptonite crystals.

Slithergee houses resemble huge honeycombs. While blind, Slithergees have an excellent sense of smell.

Mel appears to be in her 20s and the Doctor in his 40s.

The Doctor hasn't encountered the Slithergees before.

Location: Puxatawnee, 24 and 25 December 3060 and 3090.

Links: 'The Dominators' (Quarks). 'The Daleks'(anti-radiation gloves) Cloister Bell ('Logopolis', 'Castrovalva'). 'When I say run, run.' (yay!)

Untelevised Adventures: The Doctor was on Puxatawnee in 3012. The Doctor and Mel fought the Quarks on the space yacht Pinto. The Doctor starts to tell about a history-changing event that took place in 1612.

Bottom Line: "We'd better pay close attention, or we'd be completely bewildered."

A clever and yet - surprisingly! - not too confusing use of time travel, parallel universes and crossed timestreams. You'll probably need more than a single listen through (and not necessarily in the same order each time) to get this sorted out fully. Although it does help to draw a flow diagram as you listen to help make it make sense! Considering this is about parallel universes and two versions of everyone, the placement of this story in the midst of the Unbounds is rather eerie...