οἱ ἐν τῇ ξυνωμοσίᾳ

From LSJ

ἀνήρ τῷ ἀδελφῷ αὐτοῦ προσκολληθήσεται → a man cleaves each to his fellow, each to one's fellow

Source

Dutch (Woordenboekgrieks.nl)

de samenzweerders Thuc. 6.27.3 = οἱ ἐκ τῆς συνωμοσίας Plut. Ant. 13.4.