  We perform a comparative study of the ex--situ second--parameter pair
globular clusters (GCs) M30 and M92, having similar metallicities but different
horizontal branch morphologies. We obtain the similar mean primordial carbon
abundances for both clusters. However, M92 shows a large dispersion in carbon
due to a more extended C--N anticorrelation, while M30 exhibits a higher
primordial nitrogen abundance, suggesting that they have different chemical
enrichment histories. Our new results confirm our previous result that M92 is a
metal--complex GC showing a bimodal metallicity distribution. We also find that
the metal--rich group of stars in M92 shows a helium enhancement as large as
$\Delta Y$ $\sim$ 0.05 from the red giant branch bump (RGBB) $V$ magnitudes,
which can also be supported by (i) a lack of bright RGB stars, (ii) synthetic
evolutionary HB population models and (iii) the more extended spatial
distribution due to different degree of the diffusion process from their lower
masses. We reinterpret the [Eu/Fe] measurements by other, finding that the two
metallicity groups of stars in M92 have significantly different [Eu/Fe]
abundances with small scatters. This strongly suggests that they formed
independently out of well mixed interstellar media in different environments.
We suggest that M92 is a more complex system than a normal GC, most likely a
merger remnant of two GCs or a even more complex system. In Appendix, we
address the problems with the recently developed color--temperature relations
and the usage of broadband photometry in the populational taggings.
