Last night's viewing - Accused, BBC1; Bad Education, BBC3

Accused has added a new variation to television's continuing exploration of the question mark hook. First we had the Whodunit, an originating form that later gave rise to the Whydunit and the Howdunit. And now Accused cleverly trades on the seductive power of Whatthehelldidtheydo.

You know from very early on who's in the dock. But you don't know exactly what has put them there until late in the drama. You move simultaneously towards a verdict and a charge, both of them tantalisingly obscured. Last night, Anna Maxwell Martin was the accused and the puzzle was a little more knotty than usual, because she played a prison guard. She was well used to being shackled to someone else in a courtroom, but usually she was the one who had the key to the handcuffs.

Jimmy McGovern's story began where last week's episode left off, with poor deranged Stephen being admitted to a young offender institute to start his sentence. Tina is the guard who arranges his transfer and in the noisy bedlam of the prison she's the only one who notices that he might be in real danger. "Frank, I think this one's a nutter," she tells a colleague, after hearing Stephen explain how he'd stabbed his stepmother on Alastair Campbell's instructions. She suggests he's put in cell with someone who can keep an eye on him, but there are staff shortages and other distractions and Frank forgets. When Tina gets back, Stephen has hanged himself and her desperate attempts to revive him are fruitless.

The contrivance of an inescapable trap for Tina's conscience wasn't without its implausibilities. Would the system really have provided so little information about a vulnerable young prisoner? Would the arrival of Stephen's father for a prison visit, still unaware that his son was dead, have been handled so clumsily? But once he's got his characters into a bind, Jimmy McGovern is very skilled at keeping his hold. He writes for bad and weak characters as persuasively as he does for good, strong ones, which means that the hurdles he sets up for his protagonists to leap over feel solid, and can bark the shins painfully if they hit them. He doesn't forget either that banal tribulations can have large effects. In this drama a broken boiler added its weight to the tip of the scales towards disaster.

I wasn't entirely convinced by Tina's decision to say nothing when she's raped by an inmate, with Frank's collusion. A narrative feels strained when it requires two incriminating silences to unfold, even if either one taken on its own is psychologically believable. And there was something a little too neat about the impulsive crime Tina eventually commits in her distress, releasing a young prisoner at the very gates of the prison. But thanks to the quality of the dialogue and the acting – including an impressive performance by John Bishop as Stephen's grieving father – the artifice still ended up delivering real feeling.

Whether you like Bad Education, Jack Whitehall and Freddy Syborn's schoolroom comedy, will rather depend on how susceptible you are to the charms of Jack Whitehall, who plays Alfie, a feckless man/child teacher who is less interested in teaching his charges than getting them to help him win the affections of Miss Gulliver. This week, the class was off on a school field trip to the Tring Ink Museum and Petting Zoo, even less alluring than it might sound because an outbreak of worms has forced management to introduce a "look but don't touch" policy. Whitehall's character wobbles a little between a knowing cynicism and an over-contrived ingenuousness, but the comedy certainly has its moments. When the assembled pupils are asked if they have any questions by the Ink Museum's depressive manager, he gets this fine example of youthful curiosity: "Would you rather be a dog with a boy's head or a boy with a dog's head?" Takes some answering, that one.