So much of the best Singaporean theatre is born facing forwards. Plays such as Jean Tay's Everything But The Brain, The Necessary Stage's Top or Bottom and TheatreWorks' Pulse. I Am Alive. are modern, urbane, clever - they are the product of bright minds under bright lights growing hydroponically. In contrast, The Finger Players' latest production, Between the Devil and the Deep Blue Sea, feels like it was clawed from the earth.

Superficially it should feel as modern as any of them: it's set in a block of HDB flats that are about to be upgraded; there are mobile phones in it; one of the characters has studied overseas. But it gradually becomes clear that despite its contemporary setting, this play is primeval in nature: its characters are lost, guilty and sacred, like the tragic heroes of old, and they are driven by the rawest of human urges: the need to protect one's territory.

The set gives the first hint of what the play is to be about. It is a framework of aluminium tubing laid out to resemble a two-bedroom HDB flat. The tubing only delineates the edges of walls, so where the walls themselves should be there is just empty space. It seems that the flat is a cage, a space both claustrophobic, because it is small, and agoraphobic, because people can see in. Moreover, we feel that they can get in. The first vignette of the play shows random denizens of the HDB environment (schoolboys, cats and dogs, door-to-door salesgirls) walking past the flat. The masked actors play the scene for comedy, and none of them is at all threatening; however, the cumulative effect of all these passers-by is disturbing: although they respect the boundaries the aluminium tubing describes, we instinctively feel that they can see us, they can hear us, they could touch us if they wanted. They point out the impossibility of privacy, of defending one's space.

And this theme is developed and reinforced, always with intelligence, feeling and subtlety, throughout the three interconnected playlets that constitute Deep Blue Sea. Gradually we become aware that it is betrayal that has broken the walls and left us defenceless, and that only a commitment to love and trust one another can keep the outside out and the inside in. Of course the problem is that each of the three families covered in the triple bill has betrayed each other in some way.

The first of the three playlets is a revision of the first scene of Revelations, a 2003 production by The Necessary Stage. It tells of a young man recently returned from university in New York to live with his 90-year-old grandmother. He wants to go overseas again, but she is determined to keep him with her in Singapore, insisting that he take ownership of her flat. We discover that she feels responsible for the death of her grandson's parents because her irrational behaviour drove them out of her flat and into a fatal car crash years ago - and now she sees her last chance to keep what is left of her family together.

Back in 2003, this scene was easily the best part of Revelations - but since the rest of the play was dreadful, that is only lukewarm praise. This second version is much better. Playwright Chong Tze Chien (who also directs and set designs for this production) has clearly worked hard to turn a somewhat muddy script into something clean and telling; but the main improvement is in the theatricality the new version brings: where previously the mise en scène was static, almost embalmed, now it is deeply alive.

Partly the new theatricality is because of the set but mainly it is because Chong has written demons into his script. In fact the demons are in all three plays. Unseen, they tease the human inhabitants of each flat, moving furniture, opening doors and walking through walls at will. The masked actors playing the demons had calibrated their performances carefully: it would have been very easy to overplay the impish comedy of the roles - to exaggerate gestures and mug through the masks - but the actors all resisted this, and while they often allowed themselves to be funny, they never forgot to be slightly sinister with it.

The grandmother in the first playlet is the only character who is able to see the demons, although she pretty much chooses to ignore them. Goh Guat Kian's sensitive, vivid performance suggested a reason for this. She played the grandmother as tired but not frail, as if she is exhausted by work rather than age - as if she is exhausted by the burden of guilt she bears for causing her son's death. Nonetheless, she has long since reconciled herself to her burden, and she seems to accept the demon infestation as part of it, as a natural consequence of her actions.

Goh spoke in a hypnotic, sing-song voice while keeping her facial expression wearily stoical, almost blank. It should have been very odd indeed but somehow it was perfectly appropriate - it gave the impression that she had one foot already in the afterlife and was beginning to be part of some other system than ours.

The grandson cannot see the demons, though he clearly suspects something is wrong. He resents his grandmother for her neediness and her controlling behaviour - for the very things that drove his parents to their deaths - and it is his resentment as much as her guilt that has let the demons in. The most striking moment of the first playlet conveyed this powerfully. The grandmother pesters her grandson to buy her flat and he replies, "I'm only prepared to buy you a coffin!" As the old woman hears these words, she falls backwards, rigid as a corpse, helped smoothly to the ground by the demons, whom we know her grandson cannot see. His words have killed her and delivered her to the enemy... and then she continues speaking as if nothing has happened. There is a sense of mythic wrongness contained within this sequence, so that the grandson's retort feels like Lear's betrayal of Cordelia or brave Hector's flight from Achilles at the gates of Troy - and yet it is also modern, domestic and prosaic. It reminds us that our lives are epic to us because they are all we have to live.

Ian Loy, playing the grandson, was not quite a match for Goh. It felt like he hadn't fully relaxed into his character and a part of his brain was watching from the audience and making notes. It is a shame because his instincts were generally good and he enjoyed several strong moments like the one above.

In the second playlet, a rebellious 17-year-old daughter and a lecherous stepfather clash over upgrading (she wants to; he doesn't), while the mother tries to keep the peace between them and becomes increasingly convinced that her flat is haunted.

This time it is the mother's betrayals that have let the demons in. Partly it may be that she has chosen to abandon her dead husband's memory and set up house with a new man, but mainly it is that she refuses to believe her daughter, who protests innocence of a shoplifting charge and who complains of her stepfather's lasciviousness. The more she fails to trust and protect her daughter, the more her exorcism rituals - hitting a paper effigy with a shoe - are ineffectual, until eventually the demons are laughing at her and hitting her back.

Goh was back in this playlet, in the role of the mother. She brought out the childishness in this middle-aged woman, portraying her as insecure and irresponsible. In one memorable scene, she sank into an armchair, talking to herself of better times. The armchair was nothing more than a floor mat held upright by one of the demons, so essentially she was sinking into a demon's embrace. The demon rocked the chair backwards and forwards and around and Goh glowed with delight like a little girl on a satanic merry-go-round. When eventually the demon threw her off the ride and back into her world of unasked-for responsibilities - daughter, job, flat - we felt the weight pressing down on this girl-woman, and we knew she had to stand up and bear it.

She knew this too, for Goh's performance was nuanced enough to suggest that there was an adult part of the mother's soul that recognised her childishness and despised her for it, though it was unable to do anything but watch. This was virtuosic acting and it was exactly what Chong's script, written with many layers below its surface, required.

Tan Wan Sze put in an ardent performance as the daughter. She allowed a slight fragility in the defiant tilt of her head and a subtly defensive note in her caustic backchat so that we could see past the brash Ah Lian to the lost little girl underneath who does good things and bad things and needs to be loved for both.

Oliver Chong as the lecherous boyfriend acted in a different style from the others. He was considerably less naturalistic, with broader gestures and a sense of timing that seemed weighted for punchlines even when there weren't any jokes. But thematically this was the right choice. As a stepfather/boyfriend rather than a father/husband, he is an intruder into the family's space. (As the daughter keeps reminding him, he doesn't own the flat and should have no say about the proposed upgrading.) As an intruder - albeit an invited one - he is as much like the demons as he is the humans, and it is this that the bigness of Chong's performance communicated. His continuity with the demons added a sinister layer to even the broadest of his comedy, as did his facial expressions, which portrayed the slow calculations of a stupid, cunning man.

In the third playlet, a daughter is on the run from the police having embezzled from her employer, and she needs her recently retired father's CPF savings so she can escape the country and make a new life for herself elsewhere. But her father has just discovered that his wife had an affair twenty years ago, and he is not in the giving vein. Meanwhile, the police are at the door...

Ong Kian Sin as the 65-year-old retiree father showed how betrayal can turn into anger that must seem righteous to the person experiencing it, even when it is misdirected. Ong played the part with all the bluster of an impotent cuckold - he grumbled, he shouted, but he never quite confronted his daughter or his wife for their misdeeds. But yet again there were layers to the performance. Again it was clear that a part of him knew he was behaving badly, and that instead of shopping his daughter to the demon-policeman (this time a skeletal puppet eerily manipulated by the ensemble) he should protect her and give her what she needs. And when he fully realised this and attacked the demon-policeman with a cleaver, his cry of "Stop coming into my house! Will you please stop coming into my house!" was the pure, feral howl of an animal protecting its cub - and it was truly cathartic.

Goh returns again as the once-unfaithful mother in this playlet, and this time she has an easier job because, for the first time, she is not the main focus of the play. Nonetheless, her fear for her daughter, her frustration with her husband and her own sense of shame were all clearly and loudly transmitted without being histrionic.

And Tan Beng Tian as the 27-year-old embezzler daughter was believable despite being thrust into an extraordinary situation with very little in the way of build up. In a couple of places I wondered whether she quite managed to sustain the level of agitation required by her character's circumstances, but this was only true of those moments when she was more in the background, and as soon as she was in the foreground again, she was bursting with urgency.

At the end of the third playlet, the final family has redeemed its betrayals by choosing to protect each other, but the fate of the first two families remains unclear, and so the play embarks on a coda to tie up the loose ends. In a world where one's territory is so indefensible, the most generous gesture one can make is an invitation: the promise to take in and protect a stranger. One of these comes when the mother of the second family invites the grandson of the first family to dinner because his grandmother has passed away. With the thematic weight of the play behind it, this moment is incredibly touching. And the other comes just before this, when the grandmother is dying. She notices a movement outside her window and her grandson tells her it is a Western woman (Claire Devine) come to live in the now upgraded flats. The grandmother breathes a sigh of relief - this is not just an ang moh resident, it is Kuan Yin, Goddess of Mercy, come to take her to the safety of the West. Now she is ready to die. The curtains close and on them we see wayang kulit shadows of the goddess dancing, beckoning the grandmother into the afterlife. The sudden shock of this revelation, its audacity, its emotional complexity and depth, its fusion of the mundane and the mythical, and even its implied political commentary make it a mind-blowing bolt of theatre. My jaw literally dropped.

Before I sum up, a mention must go to Darren Ng's almost synaesthetic sound design, which was at its best when it showed us a landscape part primordial and part industrial, a place of dark beasts and dark machines holding each other at bay. But he managed the more hopeful moments with aplomb too, and his accompaniment to Devine's shadow dancing pushed it even further towards transcendence.

With Between the Devil and the Deep Blue Sea, The Finger Players have delivered on the potential they showed in last November's Furthest North, Deepest South and they are now the company to watch in Singapore. They have given me the kind of play the dream of which first ignited my passion for theatre: one that is intelligent, layered, truthful, intense, utterly theatrical, and acted and designed to the highest standards. For this I am and will remain grateful.