This is not so much a single dance as a recipe for producing thousands of millions of different dances in a highly prescriptive format of figures within the Celtic Brooch set, an unusual form of circular set for three couples; all the Ls perform the same movements at the same time and all the Mn similarly. Every 32-bar sequence contains the distinctive figure, The Theme, danced by the Ls in bars 1-12 and by the Mn in bars 17-28; while The Theme is being danced (by those whom the deviser, Hugh Foss, calls the "outsiders"), their partners (the "insiders") dance three complementary 4-bar figures (or, occasionally, one 12-bar figure) of which the deviser identifies 57 (and invites others to devise more). A Celtic Brooch dance is any six of these different 32-bar sequences in succession and so an immense variety of combinations is possible. Hugh Foss identifies three groups of six sequences as detailed in the separate dance instructions:
The Celtic Brooch (Elementary), The Celtic Brooch (Intermediate) and The Celtic Brooch (Advanced). He codifies and lists the 57 complementary figures. 

Note that this video is of a display consisting of only four sequences, codes 10Ax3, 43A, 21C and 30A+40A+30A followed by a choreographed exit. 

For more detail consult http://www.scottish-country-dancing-dictionary.com/dance-crib/celtic-brooch.html