In this paper, we develop a rigorously spin-adapted version of Mukherjee's state-specific multireference coupled cluster theory (SS-MRCC, also known as Mk-MRCC) [U. S. Mahapatra, B. Datta, and D. Mukherjee, J. Chem. Phys. 110, 6171 (1999)] for reference spaces comprising open-shell configurations. The principal features of our approach are as follows: (1) The wave operator Ω is written as Ω = ∑μΩμ|ϕμ〉cμ, where {ϕμ} is the set of configuration state functions spanning a complete active space. (2) In contrast to the Jeziorski–Monkhorst Ansatz in spin-orbital basis, we write Ωμ as a power series expansion of cluster operators Rμ defined in terms of spin-free unitary generators. (3) The operators Rμ are either closed-shell-like n hole-n particle excitations (denoted as Tμ) or they involve valence (active) destruction operators (denoted as Sμ); these latter type of operators can have active–active scatterings, which can also carry the same active orbital labels (such Sμ’s are called to have spectator excitations). (4) To simulate multiple excitations involving powers of cluster operators, we allow the Sμ’s carrying the same active orbital labels to contract among themselves. (5) We exclude Sμ’s with direct spectator scatterings. (6) Most crucially, the factors associated with contracted composites are chosen as the inverse of the number of ways the Sμ’s can be joined among one another leading to the same excitation. The factors introduced in (6) have been called the automorphic factors by us. One principal thrust of this paper is to show that the use of the automorphic factors imparts a remarkable simplicity to the final amplitude equations: the equations consist of terms that are at most quartic in cluster amplitudes, barring only a few. In close analogy to the Mk-MRCC theory, the inherent linear dependence of the cluster amplitudes leading to redundancy is resolved by invoking sufficiency conditions, which are exact spin-free analogues of the spin-orbital based Mk-MRCC theory. This leads to manifest size-extensivity and an intruder-free formulation. Our formalism provides a relaxed description of the nondynamical correlation in presence of dynamical correlation. Pilot numerical applications to doublet systems, e.g., potential energy surfaces for the first two excited 2A' states of asymmetric H2S+ ion and the ground 2Σ+state of BeH radical are presented to assess the viability of our formalism over an wide range of nuclear geometries and the manifest avoidance of intruder state problem.