Tori Amos sashays on in a peculiar two-sided outfit. One side has purple flowing sleeves; the other is a green, leafy affair. If she turns one way, she looks like Stevie Nicks, the other and she might be skipping around your garden. Eleven years since her mercurial 1992 debut, Little Earthquakes, nobody does "walking paradox" quite like Amos. She sings about rape and abuse, yet appears entirely comfortable doing suggestive things with a microphone.
Such curiosities (not to mention her beginnings in a dodgy metal-goth band) have long bred suspicion, but for her legions of admirers the contradictions and weaknesses are intrinsic to her appeal.
This is very much a gig for fans: songs are delivered without introduction, the audience intimate with every one. Occasionally, Amos teases them by throwing in a new arrangement (Crucify, with drum machines, is extraordinary), delaying the whoops of recognition by seconds. Preaching to the converted follows the pattern of her career (and, not uncoincidentally, that of Joni Mitchell), as she has abandoned the quest for hits in favour of various tangents.
Here, her crystal voice is drenched in echo, so that songs veer between the ethereal and the impenetrable, some of them rooted to the floor by a leaden rhythm section. She fares better alone with a piano, when her painstaking songs can breathe.
In two hours, Amos speaks just twice, which is a shame because she is very funny. One monologue refers to how her two-year-old daughter told her to "Go rock", but the songs that follow are not as interesting. The excellent Amber Waves aside, melody is largely sacrificed for melodrama. Even now, the highlights come from her early years (a pretty Cornflake Girl and a defiant, scarring Precious Things).
Still, Amos seems happy enough stretching notes into wails and beating a percussive beat on the wood of her piano, and the faithful are besotted, whatever she does. "Gig of the century," someone says.
· Tori Amos is at Hammersmith Apollo, London W6, tomorrow and Friday. Box office: 020-7416 6022.