26a Macle(an) (spot in a crystal) - Russian spy; 'an', article, dropped
23d Isiac (of Isis) - 'i' (one, in heart [of]) 'Isaac' (patriarch)
19d Stoeps (S Afr [East London] "terraces") - 'Stopes', promote; raise, 'e(cstasy)' (pill)
1a Bobac - 'ob(iit)' (Latin "died", turned) + 'bac(k)' (tail, last to go)