The end of chapter 4 of Leader's book contains a helpful summary of his Lacanian vision of the psychoses:
Paranoia: a delusion makes the world meaningful again, pinning it down; libido is localised in the Other; self and other are rigidly separated.
Schizophrenia: meaning cannot be pinned down. Libido won't stay outside and returns to invade the person's body. Invaded by the Other in their mind and body.
Melancholia: meaning is fixed; the patient is the cause of all ills; the libido submerges their self-image; Other is included within the self but does not generate battles of inclusion/exclusion.
As I read I begin to get a sense of the key conceptual players, as it were, in Lacanian discourse. Libido seems to be one of them, and what I am left with is a sense of it as a kind of Freudian primal quantum of energy, originally bodily excitation, that needs to be 'bound' by the mind. Mental illness then becomes understood as a failure of such binding through a failure of the sociodevelopmental processes which normally effect it. Rules, order, fathers, symbolism, are the agencies of transformation here. Lacan seems to provide a kind of paternal counterpart to what I am used to from Mrs Klein. We don't so much have to do with failures of containment as with failures of separation. I am still not clear though really on what libido amounts to, what it means for it to be located elsewhere (other than in the subject's own body), how it can become so persecutory or deadly in paranoia and melancholia, etc.