  A Markovian shower algorithm based on "sector antennae" is presented and its
main properties illustrated. Tree-level full-color matrix elements can be
automatically incorporated in the algorithm and are re-interpreted as
process-dependent 2 -> n antenna functions. In hard parts of phase-space, these
functions generate tree-level matrix-element corrections to the shower. In soft
parts, they should improve the logarithmic accuracy of it. The number of
matrix-element evaluations required per order of matching is 1, with an
unweighting efficiency that remains very high for arbitrary numbers of legs.
Total rates can be augmented to NLO precision in a straightforward way. As a
proof of concept, we present an implementation in the publicly available VINCIA
plug-in to the PYTHIA 8 event generator, for hadronic $Z^0$ decays including
tree-level matrix elements through ${\cal O}(\alpha_s^4)$.
