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The nature and location of the missing baryons in the universe remains a majormystery. We propose an XMM observation of a close pair of galaxy clusters oneof two pairs recently detected in SZ by ACT with possible intergalactic gasbridges between them. The other pair was observed last year. The observationwill allow the two clusters and the filament to be modeled and will provide anaverage filament temperature. The XMM image will be combined with MUSTANG-2 andACT SZ data allowing the density temperature pressure and 3D shape of thefilament to be derived. We recently used X-ray and SZ observations to study thebridge between Abell 399/401 giving the first full characterization of anintergalactic filament. These observations will constrain the nature of the missing baryons. [truncated! Please see actual data for full text]