Quantum memories offer to significantly extend the performance of quantum networks, but their complexity and limited performance at telecommunication wavelengths have so far hindered practical deployment. We propose a new memory-assisted measurement device independent quantum key distribution (MDI-QKD) protocol based on in-memory interference. Our approach leverages progress in atomic ensemble memories that enable the interference of a stationary matter qubit and a travelling photonic qubit inside a single quantum memory. We quantitatively evaluate the performance of this scheme against memoryless MDI-QKD and existing two-memory architectures, showing that it not only achieves superior secret key rates and surpasses the memoryless bound at substantially shorter distances, but also reduces hardware requirements by halving the number of memories and detectors. Our results further indicate that off resonant cascaded absorption (ORCA) memories are a particularly promising platform for implementing this protocol, and we outline a concrete design compatible with their capabilities. These findings demonstrate that in-memory interference provides a higher performance, and resource efficient route toward near term memory enhanced quantum secure communications.