"Now all I've got to do is pass as an ordinary human being. Simple. What could possibly go wrong?"
IN THIS ONE... The Doctor becomes Craig's roommate to stop a second floor from killing people.
REVIEW: A Doctor Who sitcom/romcom? Yes. I like my Doctor Who poaching from all genres, so this is exactly what the (proverbial) doctor ordered after the tearjerking Van Gogh story. I know fans who rejected the comedy because it's ridiculous for the Doctor to think kissing cheeks is the norm, or to look for buttons on an ordinary screwdriver. Naysayers, you're looking for reasons not to laugh. Look at those scenes again. Half the time, the Doctor is doing what he THINKS humans do among themselves (stuff he'd never do himself), and because he's always so intellectually lofty, well, he just doesn't look at human behavior all that closely. The other half of his shenanigans is him actively trying to sort Craig and Sophie's lives, bumbling into their relationship by design, but as if by accident. He's a fixer of things, and though he's there to investigate and stop the temporal anomalies affecting the neighborhood and his own TARDIS, he might as well help the non-couple follow their dreams.
The love story in The Lodger is really rather sweet, and of course I'd say that because I'm definitely a Craig consistently trapped in one unrequited love relationship or another, except my Sophies never reciprocate. So it's a fantasy (what romcoms aren't?), and it means that unusually for Doctor Who, the "companions" are homebodies with little of the wandering spirit required of those that board the TARDIS. It's more than soap opera, it's how the threat is defeated. We've seen other iterations of "love conquers all" in Series 5, and possibly, that's a conscious motif. It's been done badly, as with Bridwell in Victory of the Daleks, and well, as with Amy's Choice. There's just enough of a twist here for it to work well again, as Craig and Soph's relationship is based on comfort instead of wild passion, and it's wanting to stay in one place that short-circuits the so-called "Black TARDIS" (see Theories), moreso than "love". Besides, the two of them have a nice chemistry going, and they capture not just the awkwardness of their situation, but its bitter frustrations as well. They act as a sort of mirror to Amy and Rory as well, her more willing to go on an adventure, him just wanting to make a home for them, and initially seeing the Doctor as a rival before realizing the Time Lord is actually playing the Columbo of cupids.
The threat to reality is actually the B-plot, and is the weakest element. The aforementioned short-circuit is magical hand-waving when you think about it, and neither the mold nor the ship's origins are ever explained (again, see Theories). It's merely a reason for the Doctor to move in with Craig and get involved in the A-plot, while Amy is trapped aboard the TARDIS, getting up to some mildly amusing console business. But in a story like this, it's the small things that really matter. The Doctor playing Matt Smith's favorite sport with the number 11 on his jersey (goes on a bit, but not when you compare it to the cricket in Black Orchid). The joke about people blurting out their plans to the Doctor, even Craig's less than ambitious ones. Getting a cat to spy for him (unless you count Arthur the Horse, this may be the first instance of the Doctor "speaking" with an animal). The non-technological technology, a clear reference to what the 3rd Doctor makes in The Time Monster. Amy asking the Doctor to find her a fella (awwwwkward). In this context, even the telepathic headbutt passes the litmus test. Some won't agree, but it saves time, and can probably only be used because the episode is playing by comedy rules. Give in to it.
THEORIES: The strange console room seen in this episode remains a mystery, but it does make another appearance later on, in Day of the Moon. There, it is used by the Silents who have it plugged into a network of tunnels that criss-cross the Earth. That opens up many more questions, but since we do know the Silents appropriate others' technology thanks to their perception filter powers (something the mystery ship seems to also have, albeit of a different stripe), they might have stolen TARDIS tech a long time ago. Maybe the ship we see is a prototype, or a one-off they've stolen. Maybe we see it twice. Maybe, the ship we see in Day of the Moon in 1969 later ends up on top of Craig's house. The dessicated alien body inside what fans have called the "Black TARDIS" does look like it has a three-fingered hand. Could it be a Silent running from the events of that later episode (because the Moffat era takes pleasure in making the Doctor meet everyone out of order), but suffering a terrible accident?
SECOND OPINIONS: My original review, 10 and 1 Things About The Lodger, doesn't have the benefit of hindsight, so its theories take completely different turns.
REWATCHABILITY: Medium-High - I found myself completely invested in the relationships and chuckling all the way through, despite the slim plot.