The Wrong Enemy (Seven Archangels Book 4) by Jane Lebak
No one knows why Tabris, a guardian angel, killed the child he vowed to protect. The boy Sebastian got into Heaven, but the angels don't understand why Tabris isn't in Hell. Instead God's given him a second chance.
Another assignment. Another guardianship.
Although he struggles to help this new child, a tenyearold girl named Elizabeth, Tabris can't escape what he did with Sebastian. Elizabeth's coguardian doesn't trust him at all, which makes sense because even Tabris doesn't trust...