Roots: The Terminator, Star Trek
Technobabble: At the beginning of the story the Doctor deactivates the TARDIS' lateral balance plane elevation cones, disconnect the relay bypass drones and the hydraulic rams, and operates the rendel solenoid (in order to cut off all main sources of power). Later he wishes to set the coaxial stabilisers, charge the astral inducers, prime the mandrel condensers and co-ordinate the vespian transmogrifier ratchet override flangesimulator. Tegan always thought he made the names up, and it's a genuine surprise to learn he didn't.
Double Entendre: 'It's monstrous!'
Dialogue Triumphs: 'Sorry. My mistake, I pressed the wrong button.' 'Story of your life.'
'You know me, Doctor. All charm.... all heart-' '-All mouth.'
Dialogue Disasters: 'Boo!'
'Now then, do you think the good Doctor, that you could place this over his bonce, without disappearing his bonce with your amazing powers?'
Continuity: The TARDIS matter transporter is operated by one of at least two blue switches on the console. The other one helps to isolate the power supply. Also on the console is a means of turning off the interior lighting (see: 'The Sensorites'). At the time of her being collected by the Doctor Tegan was just about to have lunch. She has never heard of Sontarans. [If Tegan is still an employee of Air Australia (she wears their uniform) then we can assume she has been taken from the period between 'Time-Flight' and 'Arc of Infinity'. Of course, she doesn't refer to having had met a later incarnation when she is reunited with the fifth Doctor in that latter adventure.] The Sontarans are led by Group Marshal Nathan of the Tenth Sontaran Battle Brigade and have a Meson gun and vitrox bomb with them, which, presumably, would be effective enough to blow the TARDIS up (so it's a suicide mission?). Apart from being very effective, it also requires a great deal of power to detonate it (the Doctor assumes they intend to tap the TARDIS' main power cable). These Sontarans are much taller than others the Doctor encountered as his third and fourth selves, and more closely resemble those from 'The Two Doctors'. The TARDIS Console Room inner door has a lock. Jets of lethal gas shoot from the base of the console, killing the Sontarans. The device makes the Sontarans melt, green bile coming out of their mouths, their bodies reduced to nothing but suits and balloon like skin.
Future History: In the year 2001 a Sontaran battle fleet attacks Earth, but is defeated by the Earth Defence Force led by (a 24 year old?) Gareth Jenkins.
Untelevised Adventures: There are two Sontarans on board of a different 'race' to the most likely candidates, those of 'The Invasion of Time', so they may be survivors of an adventure which took place immediately prior to this one. [Despite its telecast occuring between 'The Two Doctors' parts two and three, judging by the length of the Doctor's hair, 'In a Fix with Sontarans' probably takes place after 'The Trial of a Time Lord', which sufficiently explains Peri's absence.] Eight-year old Gareth knows all about Doctor: he has a costume like the Doctor's (made by his Nan) and claims he saw the Doctor 'fly the TARDIS on the telly' - perhaps the Time Lord featured on a TV programme?
Location: The TARDIS, sometime before the 21st century [if the matter transporter doesn't work across timelines, this is probably 1982 from Tegan's point of view, although Gareth might be from 1985].
The Bottom Line: 'You are well and truly fixed'.
An interesting diversion made during the 1985/86 hiatus. [Nicola Bryant was unavailable hence the out-of-place appearance by Janet Fielding as Tegan.] But is it 'canon'? Since the 'fourth wall' is broken by the appearance of Jimmy Saville, possibly not. But perhaps like 'Dimensions in Time' and 'Search Out Science: The Ultimate Challenge' it is nothing but an hallucination experienced by Doctor, this time in which he believes he takes part in an obscure Earth television show called Jim'll Fix It, a programme he may have seen during his exile in the 1970s...