London buzzed with a carnival energy on the night Emily and I met for cocktails at the Hotel Café Royal. It was the evening before the Easter weekend and Piccadilly Circus milled with people who had just arrived or were just about to depart, almost everyone wheeling cases or carrying backpacks or cradling cones of spring flowers.

Something Rhymed’s April ‘challenge’ to follow in the footsteps of Agatha Christie and Dorothy L. Sayers provided the perfect excuse to embrace the city’s festive atmosphere. Surrounded by holidaymakers and all decked out in my cocktail dress, I took in afresh the grandeur of Regent Street – its buildings tall and white against the clear blue sky.

Inside the revolving doors of the Hotel Café Royal, I entered a marble lobby filled with tall vases of orchids, and the bustle of the street gave way to a hushed sense of glamour. It was easy to imagine Christie and Sayers, the Queens of Crime, meeting here with fellow members of the Detection Club, for their lavish club dinners.

Unlike the ‘shop talk’ that took up much of their usual meetings, the club’s spring and summer dinners focused more on celebration.

Now that Emily and I teach at the same university, co-write literary features and run Something Rhymed together, we have to remind ourselves to make time for purely socialising. But we long ago pledged to mark every writing success, however small. During the past few years this commitment to celebration has become more important still.

In the Green Bar, we toasted Something Rhymed over a pink champagne cocktail and a luridly blue martini, and we agreed just to chat for a while, putting off the task we’d set ourselves to compose our own set of literary rules.

We got on with that part of April’s activity in the distinctly less rarified surroundings of a Soho noodle joint, writing in between slugs of Asashi beer, and miraculously managing to avoid staining our dresses with broth.

This ramen shop brought to mind the early days of our friendship, when we both taught English in rural Japan, secretly writing in between classes. Looking back on the ways our friendship has developed since then, we realised that another unspoken ‘rule’ had developed over the years and that we had this to thank for the development of our collaboration: as well as committing ourselves to celebration we’ve also committed ourselves to candour.

I’ve learnt so much from Emily about the importance of honesty, and the courage it sometimes takes to speak the truth as we see it. This is not to say that we talk about all aspects of our lives: there remain subjects we keep to ourselves or are more likely to discuss with others. But whether we’re seeking advice on personal matters, critiquing each other’s fiction, dividing workloads, or thrashing out a line of enquiry in our collaborative writing, we always endeavour to speak our minds.

This fundamental tenet led us to formulate a few more specific rules. In terms of maintaining trust between each other, we’ll always be clear about which projects we’d like to work on together and which we’d prefer to tackle alone, and we’ve also agreed that we must never co-publish anything that we can’t both stand by. And in terms of establishing trust with our readers, we’ve promised always to acknowledge speculation.

In this way, we hope that our collaboration will thrive and, more importantly, that our friendship will endure for a lifetime.