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We target a two-tier sensor network with resource-rich master nodes at the upper tier and resource-poor sensor nodes at the lower tier. Master nodes collect data from sensor nodes and answer the queries from the network owner. The reliance on master nodes for data storage and query processing raises serious concerns about both data confidentiality and query-result correctness in hostile environments. In particular, a compromised master node may leak hosted sensitive data to the adversary; it may also return juggled or incomplete data in response to a query. This paper presents a novel spatiotemporal approach to ensure secure range queries in event-driven two-tier sensor networks. It offers data confidentiality by preventing master nodes from reading hosted data and also enables efficient range-query processing. More importantly, it allows the network owner to verify with very high probability whether a query result is authentic and complete by examining the spatial and temporal relationships among the returned data. The high efficacy and efficiency of our approach are confirmed by detailed performance evaluations.