Zagor — Sergio Bonelli Editore
Issue: #549
A volte ritornano is a sequel to the "old" story L'abisso verde ( Zagor #13 ) , published in strip form between October and November of 1963 , written by Gianluigi Bonelli and penciled by Gallieno Ferri.
Creators: Moreno Burattini, Gallieno Ferri