I loved Tigerheart's Shadow! "Romance" novels can be hard to perfect, either a hit or miss, but Erin Hunter added their own spice to it.
Okay, so...very detailed summary:
Tigerheart loves Dovewing ( Tigerheart is from ShadowClan and Dovewing is from ThunderClan). They meet at a secret place sometimes..and then a big shock comes....Dovewing is expecting Tigerheart's kits. She has a dream about a place that she believes will be safe for her and the kits. At a meeting, she tells Tigerheart she is going to go to that place, and he can leave his Clan and go with her, or stay.
They chat for a little, then they have to go back to their own separate Clans. While Tigerheart is doing something, he realizes he is late to meet Dovewing to go. He heads there, hoping to catch her, but he has to chase her scent, and when he is at the train station (there is a different name for the train station in the book) he meets a station cat named Dash.
He helps Dash chase out the cats that are stealing his food. In return, Dash helps him figure out which direction he should go to get to the Twoleg place Dovewing is heading to.
He goes there and meets Dovewing along with the group of cats that took her in- "guardian cats"- and helps them. Another group, Fog's gang, encroaches on their territory and begins stealing their food occasionally, and Tigerheart learns that they've been chased out of their original home by five foxes. He then develops a plan so that they'll leave them in peace, and participates in the attack to drive out the foxes. It involves provoking the creatures enough to lure them into the Twoleg (human) traps that have been set up around the settlement.
When the kits are weaned they travel back with some other guardian cats that want to join the Clans-including Spire, a healer that shares dreams with StarClan. Tigerheart dies and gets sent back to life by getting a leadership ceremony because he was the deputy of the leader, his father, that died. He asks if Dovewing is going to leave because he remembers that one of his lives was for loyalty, and she is surprised. The book is open-ended with Tawnypelt (his mother) saying that the days he has been absent have been dark days and there are more dark days ahead.
I hope you like the summary and are interested in the book! It's great, I tell you that. :)