In all known fermionic superfluids, Cooper pairs are composed of spin-1/2 quasi-particles that pair to form either spin-singlet or spin-triplet bound states. The "spin" of a Bloch electron, however, is fixed by the symmetries of the crystal and the atomic orbitals from which it is derived, and in some cases can behave as if it were a spin-3/2 particle. The superconducting state of such a system allows pairing beyond spin-triplet, with higher spin quasi-particles combining to form quintet or even septet pairs. We report evidence of unconventional superconductivity emerging from a spin-3/2 quasiparticle electronic structure in the topological half-Heusler semimetal YPtBi based on the linear temperature dependence of the London penetration depth, directly explained by a mixed-parity Cooper pairing model with a high-spin fermionic superfluid state. See publications for more details.