Alcohol-Induced Idiocy: Holmes gets himself and Jeremy drunk and tries to pick a fight with the older man until poor Jeremy has enough and stalks off. And directly into a kidnapping. Holmes does nothing directly stupid, but he does act like a drunken idiot.
Beware the Nice Ones: All over the place, but nowhere more startling than when the ever-affectionate-towards-his-Companions Tenth Doctor angrily manhandles a drunken Holmes.
Continuity Nod: The episode is one big nod to canonical and internal continuity, with the events of "Army of Ghosts" and "Doomsday" playing a not-so-small role in the Doctor's interactions with Torchwood.
Also, there's quite a big throwback to one brief moment in "Rose," when Clive tells Rose that the Doctor kept a family from going aboard the Titanic.
Everyone Can See It: Played with, as Beth is very aware of her feelings for Holmes and quickly confides in Sally. Ironically, the Great Detective seems to be the only one who can't see that Beth is in love with him — indeed, is quite uncertain of his own feelings for her.
Even Jeremy implies that he gets it while Holmes doesn't.
First Name Basis: Beth quickly gets into this with Holmes (despite having done it once already) and Watson, in the hopes of it being less awkward. Well, at least it works with Watson...
In Vino Veritas: When Holmes gets himself drunk, the things he says about Beth to Jeremy and the Doctor are very telling...
Jerk with a Heart of Gold: Holmes... we think. It's disturbingly hard to tell in this episode — he's certainly a far cry from the compassionate man he was a couple of episodes ago. He's not entirely a jerk in this story, but, dang, he does have some extremely cringe-worthy moments.
Jumped at the Call: Beth, pretty literally (you can hardly blame her — she's waited two years, after all).
Mistaken Identity: Poor Jeremy. A handful of Torchwood goons who can't tell the difference between him and Holmes kidnap him, thinking that he is Holmes. Fortunately for Jeremy, the Director instantly recognizes him and rectifies the situation.