In this era of 5G technology, the ever-increasing demands for high data rates lead researchers to develop hybrid satellite-terrestrial (HST) networks as a substitution to the conventional cellular terrestrial systems. Since an HST network suffers from a masking effect which can be mitigated by adopting the terrestrial relaying strategy, in this work, we focus on wireless multicasting through an HST relaying net-work (HSTRN) in which a satellite sends messages to multiple terrestrial nodes via multiple relays under the wiretapping efforts of multiple eavesdroppers. Our concern is to protect the multicast messages from being eavesdropped taking advantage of the well-known opportunistic relaying technique. We consider the satellite links follow Shadowed Rician fading whereas the terrestrial links undergo alpha-mu fading. The secrecy performance of the proposed HSTRN model is accomplished by deriving expressions for the probability of nonzero secrecy multicast capacity, ergodic secrecy multicast capacity, and secure outage probability for multicasting in closed-form. Capitalizing on the derived expressions, we analyze how a perfect secrecy level can be preserved in spite of harsh channel conditions and also present a secrecy trade-off in terms of the number of relays, multicast users, and multiple eavesdroppers. Finally, the numerical analyses are corroborated via Monte-Carlo simulations.