Forty years after decrypting and replying to an alien message the now elderly scientist who decrypted it finds her life turned upside down when a reply is received. Don Sullivan is an 87 year old retired man living with his astronomer wife Dr. Sarah Halifax in America in 2047.
On their sixtieth wedding anniversary Sarah receives an excited call from Lenore Darby, a graduate student working with SETI. Four decades earlier Sarah decoded a message from aliens in the Sigma Draconis section and now a reply has finally been received, but it is encrypted.
Soon after they receive a second unexpected message, from billionaire entrepeneur Cody McGavin, founder of McGavin Robotics. He is fascinated with space and the alien message, and believes that it message is for Sarah specifically. He reasons that advanced aliens will have the tech to lengthen their lifespans, and that the reply is therefore from the same individual alien that sent it. He believes this is a conversation between two people, not two civilizations, and he wants Sarah to live to see the next reply once they decrypt and respond.
In order for this to be possible offers to pay for her rollback treatment. Rollback is an advanced but still experimental operation that will make her young again. She agrees but only if he will also pay for Don's treatment, unwilling to leave her husband behind. Unfortunately as a side-effect of her breast cancer treatments earlier in her life the rollback doesn't work for her, and she is left an old woman while Don is made young again.
Meanwhile we see through flashbacks how the original message was received and decrypted by Sarah back in 2009. The message the aliens sent is a series of questions involving moral or ethical decisions, and they ask for a thousand individual replies.
Don is physically 25 again, and despite feeling conflicted and guilty about the apparent age gap between him and Sarah now, he is relishing his new found youth. It soon starts causing difficulties though; his hormones are back to youthful levels again as well but the physical discrepancy between him and his wife make intimacy difficult, his mental acuity is increased as well and despite himself he becomes impatient when she has trouble keeping up in casual conversation. He starts spending more time outside the house.
Don goes to pick up some papers for Sarah from from Lenore, but feeling the truth is too awkward he pretends to be his own grandson, and the two end up hitting it off and spending a lot of time together. One thing leads to another and they start an affair. Eventually Don confesses to Lenore who he really is and his true age and she kicks him out, confused and angry. Later, having thought about it she relents and they start seeing each other again for a little while until Don feels too guilty and breaks it off again.
Meanwhile Sarah is working on decoding the new message, frustrated at her mental slowness compared to when she was young and decoded the first one. She is also aware of the affair Don is having, though she doesn't know who it is with. With Don out a lot of the time she finds conversation and companionship with a nurse robot sent to look after her by Cody.
Eventually she has an epiphany and figures out the encryption code, it is based on her specific answers to the original questionnaire. Cody was right and the message is for her individually. The decoded message turns out to be the full genome for two Draconis aliens and the associated information to build and artificial womb to grow them in. The reason the message was coded to Sarah's answers is because they were testing to find a human they found morally fit to raise their children.
Sarah realizes she probably wont live long enough to raise the aliens, so she asks Don to do it in her place. He agrees, and they talk Cody into supplying the needed capital and equipment and letting them do it in their home, rather than a lab. Sarah then composes a message for the aliens explaining she doesn't have long to live but that she has found a worthy successor to raise their children. Shortly after this, she dies.
A year later the incubators are still being built but are very close to completion. Don still misses Sarah, but is starting to move on with his life. He hasn't heard from Lenore since they broke up but misses her as well. He finds out she is working at a university in New Zealand and impulsively a planet ticket and goes to see her. He tells her about Sarah decrypting the message (which is being kept secret for now) and asks her to join him raising the aliens, and possibly some children of their own. She happily agrees.
At the end of the book we fast forward to 2067, when it is calculated the aliens will be receiving Sarah's final reply. Don, Lenore, and their three children (the two aliens, and one human girl of their own) are attending a ceremony celebrating the event, and unveiling a statue honoring Sarah. But first the new family stops at the cemetery to pay their respects to the woman that brought them all together.
Best part of story, including ending:
The ideas at its core are very cool, especially the idea of sending the blueprint for building a living being as a interstellar message. However the book has tons of padding in which Don and Sarah reminisce about old sitcoms, movies, and so on. It makes for tedious reading (the entire plot of a movie is described, for instance). It's intended to make you realize how old they are, but since the references all stop at the year the book was written it makes you wonder what happened to pop culture between 2007 and 2047.
Best scene in story:
I liked the part where Sarah finally decrypts the new message and realizes what it is and that its meant for her. It is a relief and a triumph for her, and its nice for her character to get some good present-time development after most of the book showing her in flashbacks but Don in the present.
Opinion about the main character:
Don is clearly supposed to be sympathetic, and you do feel for his predicament, but the fact that he is barely young for a couple of weeks before he starts an affair, and that he maintains a huge web of lies in order to do so makes him a lot less likeable than I think Sawyer intended.