Nina Conti: a Ventriloquist's Story, BBC4, SundayDead Boss, BBC3, ThursdayLouis Theroux: Twighlight of the Porn Stars, BBC2, Sunday

A ventriloquist at a career crossroads lets her dummy show the way – to poignant effect

How about this for the plot of a horror film: a pretty young ventriloquist is bequeathed a collection of sinister-looking dolls, including one of her benefactor himself, a strange and charismatic theatrical impresario who also used to be her lover .... Freaky! OK, maybe it's a bit more straight-to-DVD than David Lynch, but this is what happened to Nina Conti.

She, daughter of Tom, had a relationship with Ken Campbell, the underground theatre maverick with eyebrows like cumulonimbi, who was 34 years her senior. As she said in her weird and beguiling memoir-cum-travelogue Nina Conti – A Ventriloquist's Story, Campbell was like "a truffle pig for other people's talents". And for some reason he took one look at Conti – a ringer for Pippa Middleton – and thought, you need to throw your voice through a small, mangy monkey puppet.

Which Conti did, successfully and wittily, for a decade, until Campbell's death in 2008 coincided with a career crisis. Going through their old correspondence, she found a note from Campbell exhorting her to attend the unlikely sounding World Ventriloquists' Convention in Kentucky. She decided to go, and yes, that event is as weird as it sounds: 300 homely-looking "vents" wandering around a grotty motel with garish puppets (aliens, newborn infants) trying to avoid those tricky plosives. (In one extraordinary sequence a fellow attendee demonstrated the art of bifurcation: moving your lips as if saying one thing while actually enunciating something entirely different.)

I don't know Conti's work well, but I liked what I saw from the film – her act seemed to extend naturally from her philosophical doubts about her vocation: at one point her monkey hypnotised its mistress whereupon it lost its voice and was forced to head-butt her back to her senses. But the clips of other performers made you wonder why you don't see more ventriloquism on these shores (it's big in America, apparently): an irresistible mix of vaudeville and metaphysics.

But as her diary-style to-camera pieces revealed, Conti was struggling. At one point she took to her motel bed to start crying on the shoulder of the Campbell puppet. The ventriloquist spilling out her guts to the hard-hearted puppet is a bit of a cliché, but Conti's "conversations" were thoughtful, funny and, in this particular scene, extraordinary. The Campbell puppet suggested bluntly to a teary Conti that her babyish monkey puppet arrived on the due day of a foetus she had aborted. No wonder she admitted she was reading a book called Problems of the Self.

No such self-doubt was apparent in the first episode of Dead Boss, which was unfortunate. The premise of this new BBC3 murder-mystery sitcom, co-written by and starring Sharon Horgan, is that Helen Stephens (Horgan) has been wrongly convicted of murdering her employer, and sentenced to 12 years in prison. Further conspiring against her are a useless solicitor, her venal sister, a sinister prison governor (Jennifer Saunders, left) and a script that displayed recidivist tendencies to criminal one-liners. Perhaps the series will settle, and the actors take a cue from Bryony Hannah's quirky turn as Helen's pyromaniac cellmate.

Talking about repeat offenders, what was Louis Theroux doing hanging around the sets of porn-film shoots again? In Twilight of the Porn Stars he was revisiting a subject, and indeed several interviewees, from a 1998 documentary he filmed in Los Angeles. This time, he was puzzling over the question of whether a career in porn might exact an emotional toll. At odds with this was his concerned-dad worry that the internet had destroyed a once-proud industry. You didn't really need to watch his film to guess the answers to those questions, but Theroux was lucky all the same to find these issues embodied in Tommy: a likeable, fortysomething leading man looking for love and a ticket out of porn and into zombie movies. Hey, everyone needs an ambition ....