Poetry-spouting zombies, psychotic ex-lovers, ancient Greeks referencing the War on Terror – Chloe Mashiter has never set herself the easiest tasks as a director. Now facing imminent graduation, the last play she has chosen to direct is on another level of tricky. Firstly, it’s the first one she’s come up with herself. But more dauntingly, it’s about a subject that is still taboo for many people – mothers who don’t, or can’t, love their children. I admit, even bringing it up in the interview made me feel uneasy, feeling the distinct taint of something unnatural and disturbing bubbling underneath our conversation. Why on earth would she choose such uniquely painful subject matter for her last show? It doesn’t stem from any personal experience.

“I procrastinate by reading the Femail section of the Daily Mail website,” says Mashiter shamefacedly. “I read the anonymous testimony of a mother who said she couldn’t make a connection with her child. And of course the Mail comments section, not the most pleasant of places, gave a wildly different set of reactions to her, some saying she should have her child taken away, others coming forward with similar stories but afraid to tell anyone. And that seemed a good place to find a drama.”

After some considerable research, including a rather awkward conversation with her own mother, who seemed unable to accept that such people existed, Mashiter set about writing the play, Unconditional, to be performed this week in Pembroke Cellars. It centres around Sarah and Daniel played by Laura Batey and Justin Wells, a young married couple who over a night of confession confront this horrific truth.

My first question is one that has been nagging at me since I heard about the play. Isn’t she writing about something she has no experience of – isn’t there a danger of coming across as trite about a very sensitive issue? She realises this problem, but in fact says the problem is much more universal. “It’s about what happens when everyone expects something of you you cannot live up to. I’ve done my research, and I try to leave my judgment out of it.” She has also tried to stop it becoming too dramatic and shouty. “The dialogue explores the tiny details of the relationship – it isn’t just talking about the issue for hours on end.”

How do you get the actors to deal with this massive challenge, playing people not so much older than themselves, but massively emotionally removed? Mashiter has afforded the two of them time to improvise, spending a lot of time building up the characters from the inside out, including showing them pictures of the supposed child that causes the rift, as well as working from the outside in, producing the new characters “muscle by muscle”. It is hard for Mashiter to see them reinterpret her creations, but they have slowly but surely replaced the original images in her head, for which she is actually very thankful. “You don’t talk to the actors about being mad or having mental problems,” she says. “You talk about 3D, rounded characters. And the drama comes from real people, not people talking deliberately about issues.”

Mashiter wanted to do some original work before she left, but the style is rather different than her usual more physical pieces. It did, however, afford her a chance to use the Pembroke Cellars in a new way, using the low ceiling and open space to create a domestic environment, full of sofas, so that the audience felt intimate with these characters, essential for the sense of real drama. The Pembroke Cellars are a lovely venue, though she wishes it could have more of the exposure to Cambridge audiences that the Corpus Playroom now has, “One does not simply wander into the Cellars.”