Doctor Jackman is on the run, but he can't escape himself. Waking up in a seaside hotel with his chain around his ankle and its key in a box locked with a combination only he knows, he finds Mr Hyde has been out to play during the night and has decided to teach him a lesson for leaving him restrained. Not only has he not slept the entire night, so Jackman too is exhausted, but there's a message scrawled on the wall in his own blood: "When you sleep I will eat your children." I think Doctor Jackman has finally found a cure for narcolepsy.

Knowing he can't run any more, Jackman takes a train ride. He calls his wife to check that she and the kids are safe, and his minder, Katherine Reimer, to report that Hyde seems to be increasingly testy. Miranda Callendar and her partner are installed in the bunker too, and try to warn Jackman to turn off his phone. Benjamin's high-tech surveillance unit is on his trail and trace his mobile phone signal to the train. It's enough for them to work out where he's going - Syme's house.

Jackman ties Syme to a chair and shuts him in the basement, intending to find out exactly what part he's been playing in the mystery, but as Hyde begins to make his appearance Jackman realises that the "friend" Claire said she was staying with is Syme, and she's about to witness his transition. He locks the cellar door, but Hyde, blinking in and out of consciousness, discovers the combination to the key box. Just in time Jackman forces Syme to swallow the key instead.

Hyde's pissed about losing the key, but intrigued to find Claire there. They circle each other like wary panthers, Hyde almost certain of his supremacy but Claire refusing to back down, which excites him even more. Just as things are about to get really interesting Benjamin arrives with a SWAT team. Even though Hyde is already in the ascendent, Benjamin taunts him with threats to Jackman's children. He lives to regret this move, but not for long as the lightning-quick Hyde opens his carotid arteries and bids him farewell. The rest of the team don't take much persuading to allow Hyde to escape.

The next day Jackman awakes outside Syme's house covered in blood and with a key clenched in his hand. His memory returns in bursts, leading him to believe first that he has killed Syme and second his wife. Before his memory is fully restored, he gives himself up to the police who take him in for questioning. While he's in custody the surveillance team resurface and frog-march him out to a waiting van, where Claire is chained and gagged and a techno-coffin awaits to transport him and his dangerous alter-ego to who knows where.

On one level, not much happened in tonight's third instalment, and yet the story gripped from the off, with clever use of flashback to explain Jackman's slowly returning memory of the events of the night before and ensure the tension was maintained at its highest. The irritating Benjamin ("Listen up English people" - yuk) was despatched with great finesse to loud cheers in our house but not before the hunt for Jackman/Hyde was revealed as the culmination of a 100-year plot. Someone, some very powerful someone, believes they can harness Hyde as a weapon and they'll always be able to rein him in eventually when he flips back to Jackman. But it became clear tonight but neither they nor even Hyde himself knows exactly how dangerous or how fast he is.

The smouldering sexual tension between Claire and the man who appears to be at the same time her husband AND everything she really wants her husband to be was well done, but I wouldn't be surprised to learn she's playing some part in the plot. And we're still waiting to learn how Jackman came to be alive at all, given the original Dr Jekyll died childless.

The real revelation of the evening though, mentioned so briefly and glibly that you could almost have missed it, was that there is a cure for Jackman's condition - and has been for fifty years.