  Almost three decades ago, the Fly's Eye experiment recorded the most
energetic cosmic-ray ever observed. With an energy of 320 EeV, this event is
well beyond the suppression region of the ultra-high energy cosmic rays (UHECR)
spectrum. Modern and larger observatories, with an exposure up to 60 times
larger, have never observed an event with even remotely comparable energy.
Thus, if the energy of the Fly's Eye event was indeed well measured, as
strongly suggested by the data, then it remains a great mystery or an
unbelievable stroke of luck. At such high energies, the Universe is very opaque
to electromagnetic interacting particles, whether photons, protons or heavy
nuclei, and therefore its source must be relatively close. Using numerical
simulations for the propagation of protons and nuclei, we reexamine the problem
by testing different possibilities for the nature of the primary, the injection
spectrum and the location of the source. Based on these calculations, we show
that the most feasible scenario corresponds to a nearby ($\sim 2-3$ Mpc)
bursting source of heavy nuclei in the northern sky, which injected a hard
spectrum ($\gamma \le 1.5$) with an energy cut-off between $300$ and $1000$
EeV. Such scheme generates a significant probability for the observation of one
event by Fly's Eye combined with a null result of Telescope Array at the same
energy.
