Anyone who insists twice that something is harmless has usually given us a reason to worry. Peter John Dean's "Celtic" is built on that instinct. Its speaker announces, "They are not sinister ghosts," then repeats the claim with a nervous "Oh no!" The rest of the poem quietly takes the claim apart.
On the surface, the poem describes pale, smiling spirits who appear at twilight and sing to passing travellers. The final stanza turns to the reader: in the islands, "you may see many travellers / Who, long ago hearing them sing, / Are now old stones." The central idea is that menace does not have to look menacing. The ghosts are lovely, soft-footed and musical, and that gentleness is the trap. Their beauty is how they hunt.
The imagery works by draining colour and substance away. The ghosts have "pale hair" and "pale lips," and in the second stanza they are "paler than rain." Rain is already close to colourless, so being paler than it suggests something almost not there. Then the "pale lips smiling" return as "bloodless lips," and the same detail turns from charming to corpse-like. The third stanza goes further: winds blow "through their hollow bones." Judging by the imagery, this may hint at where the music comes from. Wind passing through hollow bones is rather like breath through a pipe, so the "distant songs" may be the ghosts' emptiness made audible. That is only a suggestion, but the poem invites it.
Word choice carries a lot of the unease. "Charm" is the key verb, and it works two ways: to delight and to put under a spell. The songs are "distant," so they are always a little further on and always drawing the traveller forward. The feet "murmur in the grass," a lovely phrase that gives footsteps a voice and makes the ghosts' movement sound like whispering. Even the word "sinister" works against the speaker, since its hissing sounds are echoed in "ghosts," "smiling," "songs" and "grass." The poem has a hush to it, as if the reader is being lulled in the same way as the travellers.
Structurally, the poem is free verse. It has no rhyme and no regular metre, and its lines are short, mostly with two to four stressed syllables. Repetition does the work that rhyme might otherwise do. "Pale" recurs, the phrase "not sinister ghosts" returns, and "lips" ends both the first and second stanzas. This gives the poem the feel of a charm or lullaby while leaving it unresolved, with no tidy chime to close any stanza. The stanzas also vary in length, from five lines to two. The shortest, "They are not sinister ghosts, / Oh no!", interrupts the slow, floating pace like a sudden intake of breath. The exclamation sounds almost cheerful, and the cheerfulness is the problem. It reads like someone reassuring a child, or themselves, a little too quickly.
The last stanza changes the poem's whole perspective. Up to this point the poem speaks of "they," the ghosts, in the present tense. Now it addresses "you" and looks back to "long ago." The tone stays calm and matter-of-fact, almost like a tourist guide: "you may see many travellers." The horror is delivered without any alarm. The final line, "Are now old stones," is made of short, heavy words that land like three beats on a drum. Stones are the opposite of song: hard, silent, unmoving. The word "old" adds centuries of stillness to the travellers' fate. A reader might picture the standing stones or rocky shapes of an island landscape, though the poem never says so. The title "Celtic" sets the story in a place of old legend, and the idea of people becoming part of the land suits that setting.
What makes the poem worth reading is its restraint. It never describes the moment of transformation, never lets a ghost snarl, and never raises its voice except in that suspicious "Oh no!" Because the ghosts are never openly threatening, the poem leaves the reader in the position of the traveller. We have been told not to worry, and we are listening to the song anyway.