One of the many realisations you discover upon becoming the owner of a young, wild cat is that your conscience will never be the same again. Every night you become, indirectly accessory to some crime or other. These vary in their degree and type; sometime it is the indignity of discovering a poor, blind baby mouse trodden into your carpet, or the entrails of some anonymous prey cast onto your companion lid, or, as has been the case most recently, finding the carcasses of small, glaucose, white-bellied frogs delivered propitiously onto your bathroom floor.

When Behemoth is embracing the wilder side of her nature, she enjoys returning home with trophies. This is not unusual, and almost every cat owner will have similar semi-tragic stories to tell: of the mouse cadeaux; of the little bird corpse left turgid, feet-upright on the doorstep or on the kitchen floor. But Behemoth is not as good a hunter as she might like to believe; often her prey are not yet dead. Whether this is because – like a maliciously playful Roman emperor – she desires to draw out and the moment of death till its excruciatingly climax, or whether she is simply ineffectual, is impossible to know.

A few times Behemoth has jumped through the hatch with a tiny mouse wriggling in her jaws. Comic scenes have ensued. The cat drops the mouse, I jump onto a chair, Gideon tries to pounce on the mouse to stop it from disappearing in the boat – the cat is in hot pursuit. Funnily enough, both times this has happened Gideon has proved himself to be the better hunter, catching the mouse before Behemoth has even had a look-in.

So Behemoth, being the fiendish and nefarious creature that she is, has little regard for the animal and reptilian populations that depend so fragilely upon life on the river-bank. Night-time for her, is hunting time, and it has not been uncommon to discover her leaping across our sleeping bodies from the cottage window, with an as-yet live victim throbbing in her small, clenched jaw.

During winter we could contain the problem, and as we have no cat-flap (expensive, tricky and insecure to install as it is), we clamped the windows shut and thereby doomed Behemoth to prowl belligerently indoors. But now, come Summer, when the boat becomes dusty and stifling at night, we have no choice but to leave windows open, and so our small demon-Diana has been able to feast as gluttonously upon the lesser mammals as she wishes, roaming about the precincts adjacent to the boat.

Being responsible for the life of a small cat has entailed many shifts in the habits and patterns of our boat life. For example, when we choose a mooring we do not only have our own wishes to consider, a secondary question is always would Behemoth like it here? I scan to see that a mooring meets our requirements: is there space for her to play and roam? Are there trees for her to climb and shrubbery to conceal herself in if she desires to hide from the incessant tow-path traffic of intrepid bicycles and large, inquisitive dogs? But often her needs coincide with ours, as it is always pleasanter to moor beside the green spaces of Victoria Park or Hackney Marshes than the more crowded thoroughfares of Kings Cross and Camden Town.

Frogs are her new fascination. Last night, while Gideon was away in Sheffield and I was lying in bed, on a night which would transpire to be my last as a teacher, I was wakened several times by her plaintive mewing. In my half-delirious, somnolent state, I found it difficult to locate where she was, unsure at first if she was baying by the cottage window in the prow (as she was wont to do in winter, as a signal that she wished to retire for the night and be let back in), or if she was beside the small window by our wardrobe. When I peeled back the light duvet, and groped my way out of bed I discovered her in the bathroom – an uncommon place for a cat. Her glittering gold-green eyes looked piteously up at me, so that when I spied the prone body of a small, white-bellied frog at her feet, I was unsure if she was proud of her kill or heartily ashamed of it. The dear, small frog was dead but not mutilated, he had been brought back to the boat as an offering – a token. But Behemoth, her expression so unreadable and at odds with her act, looked as confounded by her position as I was. It was a dumb, primordial act of killing: a reflex for a creature who loves the rush of pursuit and capture; killing more in the spirit of play than material necessity.

Three times that night I awoke, three times deposited the small, limp cadavers of white-bellied frogs from out of my bathroom window. Behemoth would not cease.

Over the months, Gideon and I have become quite expert at capturing mice, sometimes Gideon joked, more effective than Behemoth herself. Often she would bring live-specimens back to the boat, and Gideon and I afraid of an infestation on our small living container would exercise all our ingenuity to catch it, before it had eluded the cat and sought refuge in some small, inaccessible space beneath the floorboards or in the tool cupboard.

On one memorable occasion in the winter, I remember unconsciously reaching for a piece of wood behind me as I stacked the fire. Instead of the expected rough, hard texture of wooden off-cuts, I scooped up the body of a small, soft mouse in a state of partial bodily decomposition. It was not a nice surprise! On another occasion, during one of Behemoth’s sprightly leaps across the bed in the sleeping cabin from the cottage window we discovered the body of a small, squirming mouse on the pillow beside us – fallen from her jaws mid-flight.

But for all these bloody incidents, my love and respect for the small, tenacious creature has not diminished one jot. Her feline instincts, her beguiling, beautiful face; her stripy flank and slinking manner elicit a daily joy in me, that feed and nourish me my spirits when they are low or are in need of some comic, absurd or wonderful distraction.