The Phoenix / Tilly Bagshawe.

"Ella Praeger has always felt like an outsider. So when she is called to join the ranks of The Group, a force for good operating in the shadows, her world shifts. She is gifted a purpose - and a dangerous legacy. Years ago, The Group rid the world of one of its most powerful criminal masterminds. Yet when a child washes up on a beach in Greece, a mysterious symbol tattooed on its heel, it is a clear warning: impossibly, Athena Petridis has returned to reclaim her empire.Ella's connection to Athena is deeply personal. Thrown into an underworld of treachery and corruption, and haunted by the tragedies of her own past, Ella is reborn as an agent, chasing a villain risen from the ashes. But only one of them can fulfil their destiny..."--Publisher description.