I am assuming the house has wood lath. Break about out two inches of plaster around the hole so that there is some lath exposed. Screw and/or wire tie metal lath to the wood lath. Paint the edges of the existing plaster with a polyvinyl acetate bonding agent. Plaster the hole just shy of flush with Structolite or Gypsolite. The easiest way to do this is to fill it full then screed it off flush using the existing ceiling as grounds then cut it back about an eighth inch with the edge of the trowel. Finish it with RedTop finish plaster or Diamond finish or Kak-Kote finish to match the existing.